CHAPTER IX
THE RECOIL CHECK
"Who is that?" asked Ned Newton, with a quick glance at his chum.
"I don't know," Tom answered. "I left orders we weren't to be disturbedunless it was something important."
"May be something has happened," suggested the navy officer, "anotherfire, perhaps, or a--"
"It isn't a fire," Tom answered. "The automatic alarm would be ringingbefore this in that case."
The knock was repeated. Tom went softly to the door and opened itquickly, to disclose, standing in the corridor, one of the messengersemployed about the shops.
"Well, what is it?" asked Tom a bit sharply.
"Oh, if you please, Mr. Swift," said the boy, "a man has applied forwork at the main office, and you know you left orders there that if anymachinists came along, we were to--"
"Oh, so I did," Tom exclaimed. "I had forgotten about that," he went onto Lieutenant Marbury and Ned. "I am in need of helpers to rush throughthe finishing touches on my aerial warship, and I left word, if anyapplied, as they often do, coming here from other cities, that I wantedto see them. How many are there?" Tom asked of the messenger.
"Two, this time. They both say they're good mechanics."
"That's what they all say," interposed Tom, with a smile. "But, thoughthey may be good mechanics in their own line, they need to have specialqualifications to work on airships. Tell them to wait, Rodney," Tomwent on to the lad, "and I'll see them presently."
As the boy went away, and Tom closed the door, he turned to LieutenantMarbury.
"You were about to give me another warning when that interruption came.You might complete it now."
"Yes, it was another warning," spoke the officer, "and one I hope youwill heed. It concerns yourself, personally."
"Do you mean he is in danger?" asked Ned quickly.
"That's exactly what I do mean," was the prompt reply. "In danger ofpersonal injury, if not something worse."
Tom did not seem as alarmed as he might reasonably have been under thecircumstances.
"Danger, eh?" he repeated coolly. "On the part of whom?"
"That's just where I can't warn you," the officer replied. "I can onlygive you that hint, and beg of you to be careful."
"Do you mean you are not allowed to tell?" asked Ned.
"No, indeed; it isn't that!" the lieutenant hastened to assure theyoung man. "I would gladly tell, if I knew. But this plot, like theother one, directed against the inventions themselves, is so shroudedin mystery that I cannot get to the bottom of it.
"Our Secret Service men have been working on it for some time, not onlyin order to protect you, because of what you have done for thegovernment, but because Uncle Sam wishes to protect his own property,especially the searchlight and the big cannon. But, though our agentshave worked hard, they have not been able to get any clues that wouldput them on the right trail.
"So we can only warn you to be careful, and this I do in allearnestness. That was part of my errand in coming here, though, ofcourse, I am anxious to inspect the new aerial warship you haveconstructed. So watch out for two things--your inventions, and, morethan all, your life!"
"Do you really think they would do me bodily harm?" Tom asked, a trifleskeptical.
"I certainly do. These foreign spies are desperate. If they cannotsecure the use of these inventions to their own country, they aredetermined not to let this country have the benefit of them."
"Well, I'll be careful," Tom promised. "I'm no more anxious than anyoneelse to run my head into danger, and I certainly don't want any of myshops or inventions destroyed. The fire in the red shed was as close asI want anything to come."
"That's right!" agreed Ned. "And, if there's anything I can do, Tom,don't hesitate to call on me."
"All right, old man. I won't forget. And now, perhaps, you would liketo see the Mars," he said to the lieutenant.
"I certainly would," was the ready answer. "But hadn't you better seethose men who are waiting to find out about positions here?"
"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 thatit is not yet completed, and only recently did I begin to solve theproblem of mounting the guns. So be a little easy with yourcriticisms."
Followed by Ned and Lieutenant Marbury, Tom led the way into the bigairship shed. There, swaying about at its moorings, was the immenseaerial warship. To Ned's eyes it looked complete enough, but, when Tompointed out the various parts, and explained to the government officerhow it was going to work, Ned understood that considerable yet remainedto be done on it.
Tom showed his official guest how a new system of elevation anddepressing rudders had been adopted, how a new type of propeller was tobe used and indicated several other improvements. The lower, or cabin,part of the aircraft could be entered by mounting a short ladder fromthe ground, and Tom took Ned and Lieutenant Marbury through theengine-room and other compartments of the Mars.
"It certainly is most complete," the officer observed. "And when youget the guns mounted I shall be glad to make an official test. Youunderstand," he went on, to Tom, "that we are vitally interested in theguns, since we now have many aircraft that can be used purely forscouting purposes. What we want is something for offense, a veritablenaval terror of the seas."
"I understand," Tom answered. "And I am going to begin work on mountingthe guns at once. I am going to use the Newton recoil check," he added."Ned, here, is responsible for that."
"Is that so?" asked the lieutenant, as Tom clapped his chum on the back.
"Yes, that's his invention."
"Oh, it isn't anything of the sort," Ned objected. "I just--"
"Yes, he just happened to solve the problem for me!" interrupted Tom,as he told the story of the door-spring.
"A good idea!" commented Lieutenant Marbury.
Tom then briefly described the principle on which his aerial warshipwould work, explaining how the lifting gas would raise it, with itsload of crew, guns and explosives, high into the air; how it could thenbe sent ahead, backward, to either side, or around in a circle, bymeans of the propellers and the rudders, and how it could be raised orlowered, either by rudders or by forcing more gas into the liftingbags, or by letting some of the vapor out.
And, while this was being done by the pilot or captain in charge, thecrew could be manning the guns with which hostile airships would beattacked, and bombs dropped on the forts or battleships of the enemy.
"It seems very complete," observed the lieutenant. "I shall be gladwhen I can give it an official test."
"Which ought to be in about a week," Tom said. "Meanwhile I shall beglad if you will be my guest here."
And so that was arranged.
Leaving Ned and the lieutenant to entertain each other, Tom went to seethe mechanics who had applied for places. He found them satisfactoryand engaged them. One of them had worked for him before. The other wasa stranger, but he had been employed in a large aeroplane factory, andbrought good recommendations.
There followed busy days at the Swift plant, and work was pushed on theaerial warship. The hardest task was the mounting of the guns, andequipping them with the recoil check, without which it would beimpossible to fire them with the craft sailing through the air.
But finally one of the big guns, and two of the smaller ones were inplace, with the apparatus designed to reduce the recoil shock, and thenTom decided to have a test of the Mars.
"Up in the air, do you mean?" asked Ned, who was spending all his sparetime with his chum.
"Well, a little way up in the air, at least," Tom answered. "I'll makea sort of captive balloon of my craft, and see how she behaves. I don'twant to take too many chances with that new recoil check, though itseems to work perfectly in theory."
The day came when, for the first time, the Mars was to come out of thebig shed where she had been constructed. The craft was not compl
etedfor a flight as yet, but could be made so in a few days, with rushwork. The roof of the great shed slid back, and the big envelopecontaining the buoyant gas rose slowly upward. There was a cry ofsurprise from the many workmen in the yard, as they saw, most of themfor the first time, the wonderful new craft. It did not go up veryhigh, being held in place with anchor ropes.
The sun glistened on the bright brass and nickel parts, and glintedfrom the gleaming barrels of the quick-firing guns.
"That's enough!" Tom called to the men below, who were paying out theropes from the windlasses. "Hold her there."
Tom, Ned, Lieutenant Marbury and Mr. Damon were aboard the captive Mars.
Looking about, to see that all was in readiness, Tom gave orders toload the guns, blank charges being used, of course.
The recoil apparatus was in place, and it now remained to see if itwould do the work for which it was designed.
"All ready?" asked the young inventor.
"Bless my accident insurance policy!" exclaimed Mr. Damon. "I'm asready as ever I shall be, Tom. Let 'em go!"
"Hold fast!" cried Tom, as he prepared to press the electrical switchwhich would set off the guns. Ned and Lieutenant Marbury stood near theindicators to notice how much of the recoil would be neutralized by thecheck apparatus.
"Here we go!" cried the young inventor, and, at the same moment, fromdown below on the ground, came a warning cry:
"Don't shoot, Massa Tom. Don't shoot! Mah mule, Boomerang--"
But Eradicate had spoken too late. Tom pressed the switch; there was adeafening crash, a spurt of flame, and then followed wild cries andconfused shouts, while the echoes of the reports rolled about the hillssurrounding Shopton.