CHAPTER VII
WARNINGS
For a moment or two Tom Swift did not seem to comprehend what Ned hadsaid. He remained staring, first at his chum, who stood pointing, andfrom him Tom's gaze wandered to the top of the door. It may have been,and probably was, that Tom was thinking of other matters at thatinstant. But Ned said again:
"Wouldn't that do, Tom? Check the recoil of the gun with whatever stuffis in that arrangement!"
A sudden change came over Tom's face. It was lighted up with a gleam ofunderstanding.
"By Jove, Ned, old man!" he cried. "I believe you've struck it! And tothink that has been under my nose, or, rather, over my head, all thiswhile, and I never thought of it. Hurray! That will solve the problem!"
"Do you think it will?" asked Ned, glad that he had contributedsomething, if only an idea, to Tom's aerial warship.
"I'm almost sure it will. I'll give it a trial right away."
"What's in that door-check?" Ned asked. "I never stopped before tothink what useful things they are, though at the bank, with the big,heavy doors, they are mighty useful."
"They are a combination of springs and hydrostatic valves," began Tom.
"Good-night!" laughed Ned. "Excuse the slang, Tom, but what in theworld is a hydrostatic valve?"
"A valve through which liquids pass. In this door-check there may be amixture of water, alcohol and glycerine, the alcohol to preventfreezing in cold weather, and the glycerine to give body to the mixtureso it will not flow through the valves too freely."
"And do you think you can put something like that on your guns, so therecoil will be taken up?" Ned wanted to know.
"I think so," spoke Tom. "I'm going to work on it right away, and we'llsoon see how it will turn out. It's mighty lucky you thought of that,for I sure was up against it, as the boys say."
"It just seemed to come to me," spoke Ned, "seeing how easily the doorclosed."
"If the thing works I'll give you due credit for it," promised Tom."Now, I've got to figure out how much force a modified hydrostaticvalve check like that will take up, and how much recoil my biggest gunwill have."
"Then you're going to put several guns on the Mars?" asked Ned.
"Yes, four quick-firers, at least, two on each side, and heavier gunsat the bow and stern, to throw explosive shells in a horizontal orupward direction. For a downward direction we won't need any guns, wecan simply drop the bombs, or shells, from a release clutch."
"Drop them on other air craft?" Ned wanted to know.
"Well, if it's necessary, yes. Though I guess there won't be muchchance of doing that to a rival aeroplane or dirigible. But in flyingover cities or forts, explosive bombs can be dropped very nicely. Foruse in attacking other air craft I am going to depend on my lateralfire, from the guns mounted on either beam, and in the bow and stern."
"You speak as though you, yourself, were going into a battle of theair," said Ned.
"No, I don't believe I'll go that far," Tom replied. "Though, if thegovernment wants my craft, I may have to go aloft and fire shots attargets for them to show them how things work.
"Please don't think that I am in favor of war, Ned," went on Tomearnestly. "I hate it, and I wish the time would come when all nationswould disarm. But if the other countries are laying themselves out tohave aerial battleships, it is time the United States did also. We mustnot be left behind, especially in view of what is taking place inEurope."
"I suppose that's right," agreed Ned. "Have you any of your guns ready?"
"Yes, all but the mounting of them on the supports aboard the Mars. Ihaven't dared do that yet, and fire them, until I provided some meansof taking up the recoil. Now I'm going to get right to work on thatproblem."
There was considerable detailed figuring and computation work ahead ofTom Swift, and I will not weary you by going into the details of highermathematics. Even Ned lost interest after the start of the problem,though he was interested when Tom took down the door-check and beganmeasuring the amount of force it would take up, computing it on scalesand spring balances.
Once this had been done, and Tom had figured just how much force couldbe expected to be taken up by a larger check, with stronger hydrostaticvalves, the young inventor explained:
"And now to see how much recoil force my guns develop!"
"Are you really going to fire the guns?" asked Ned.
"Surely," answered Tom. "That's the only way to get at real results.I'll have the guns taken out and mounted in a big field. Then we'llfire them, and measure the recoil."
"Well, that may be some fun," spoke Ned, with a grin. "More fun thanall these figures," and he looked at the mass of details on Tom's desk.
This was the second or third day after the fire in the red shed, and inthe interim Tom had been busy making computations. These were aboutfinished. Meanwhile further investigation had been made of cluesleading to the origin of the blaze in the shed, but nothing had beenlearned.
A photo-telephone had been installed near Eradicate's quarters, in thehope that the mysterious stranger might keep his promise, and come tosee about the mule. In that case something would have been learnedabout him. But, as Tom feared, the man did not appear.
Ned was much interested in the guns, and, a little later, he helped Tomand Koku mount them in a vacant lot. The giant's strength came in handyin handling the big parts.
Mr. Swift strolled past, as the guns were being mounted for thepreliminary test, and inquired what his son was doing.
"It will never work, Tom, never!" declared the aged inventor, wheninformed. "You can't take up those guns in your air craft, and firethem with any degree of safety."
"You wait, Dad," laughed Tom. "You haven't yet seen how the Newtonhydrostatic recoil operates."
Ned smiled with pleasure at this.
It took nearly a week to get all the guns mounted, for some of themrequired considerable work, and it was also necessary to attach gaugesto them to register the recoil and pressure. In the meanwhile Tom hadbeen in further communication with government experts who were soon tocall on him to inspect the aerial warship, with a view to purchase.
"When are they coming?" asked Ned, as he and Tom went out one morningto make the first test of the guns.
"They will be here any day, now. They didn't set any definite date. Isuppose they want to take us unawares, to see that I don't 'frame-up'any game on them. Well, I'll be ready any time they come. Now, Koku,bring along those shells, and don't drop any of them, for that newpowder is freakish stuff."
"Me no drop any, Master," spoke the giant, as he lifted the boxes ofexplosives in his strong arms.
The largest gun was loaded and aimed at a distant hill, for Tom knewthat if the recoil apparatus would take care of the excess force of hislargest gun, the problem of the smaller ones would be easy to solve.
"Here, Rad, where are you going?" Tom asked, as he noticed the coloredman walking away, after having completed a task assigned to him.
"Where's I gwine, Massa Tom?"
"Yes, Rad, that's what I asked you."
"I--I'se gwine t' feed mah mule, Boomerang," said the colored manslowly. "It's his eatin' time, jest now, Massa Tom."
"Nonsense! It isn't anywhere near noon yet."
"Yais, sab, Massa Tom, I knows dat," said Eradicate, as he carefullyedged away from the big gun, "but I'se done changed de eatin' hours obdat mule. He had a little touch ob indigestion de udder day, an' I'sefeedin' him diff'rent now. So I guess as how yo'll hab t' 'scuse menow, Massa Tom."
"Oh, well, trot along," laughed the young inventor. "I guess we won'tneed you. Is everything all right there, Koku?"
"All right, Master."
"Now, Ned, if you'll stand here," went on Tom, "and note the extremepoint to which the hand on the pressure gauge goes, I'll be obliged toyou. Just jot it down on this pad."
"Here comes someone," remarked the bank clerk, as he saw that hispencil was sharpened. He pointed to the field back of them.
"It's Mr. Damon," observe
d Tom. "We'll wait until he arrives. He'll beinterested in this."
"Bless my collar button, Tom! What's going on?" asked the eccentricman, as he came up. "Has war been declared?"
"Just practicing," replied the young inventor. "Getting ready to putthe armament on my aerial warship."
"Well, as long as I'm behind the guns I'm all right, I suppose?"
"Perfectly," Tom replied. "Now then, Ned, I think we'll fire."
There was a moment of inspection, to see that nothing had beenforgotten, and then the big gun was discharged. There was a loudreport, not as heavy, though, as Ned had expected, but there was nopuff of smoke, for Tom was using smokeless powder. Only a little flashof flame was observed.
"Catch the figure, Ned!" Tom cried.
"I have it!" was the answer. "Eighty thousand!"
"Good! And I can build a recoil check that will take up to one hundredand twenty thousand pounds pressure. That ought to be margin of safetyenough. Now we'll try another shot."
The echoes of the first had hardly died away before the second gun wasready for the test. That, too, was satisfactory, and then the smallerones were operated. These were not quite so satisfactory, as the recoildeveloped was larger, in proportion to their size, than Tom had figured.
"But I can easily put a larger hydrostatic check on them," he said."Now, we'll fire by batteries, and see what the total is."
Then began a perfect bombardment of the distant hillside, servicecharges being used, and explosive shells sent out so that dirt,stones and gravel flew in all directions. Danger signs and flags hadbeen posted, and a cordon of Tom's men kept spectators away from thehill, so no one would be in the danger zone.
The young inventor was busy making some calculations after the last ofthe firing had been completed. Koku was packing up the unfired shells,and Mr. Damon was blessing his ear-drums, and the pieces of cotton hehad stuffed in to protect them, when a tall, erect man was observedstrolling over the fields in the direction of the guns.
"Somebody's coming, Tom," warned Ned.
"Yes, and a stranger, too," observed Tom. "I wonder if that can beEradicate's Frenchman?"
But a look at the stranger's face disproved that surmise. He had afrank and pleasant countenance, obviously American.
"I beg your pardon," he began, addressing everyone in general, "but Iam looking for Tom Swift. I was told he was here."
"I am Tom Swift," replied our hero.
"Ah! Well, I am Lieutenant Marbury, with whom you had somecorrespondence recently about--"
"Oh, yes, Lieutenant Marbury, of the United States Navy," interruptedTom. "I'm glad to see you," he went on, holding out his hand. "We arejust completing some tests with the guns. You called, I presume, inreference to my aerial warship?"
"That is it--yes. Have you it ready for a trial flight?"
"Well, almost. It can be made ready in a few hours. You see, I havebeen delayed. There was a fire in the plant."
"A fire!" exclaimed the officer in surprise. "How was that? We heardnothing of it in Washington."
"No, I kept it rather quiet," Tom explained. "We had reason to suspectthat it was a fire purposely set, in a shed where I kept a quantity ofexplosives."
"Ha!" exclaimed Lieutenant Marbury. "This fits in with what I haveheard. And did you not receive warning?" he asked Tom.
"Warning? No. Of what?"
"Of foreign spies!" was the unexpected answer. "I am sorry. Some ofour Secret Service men unearthed something of a plot against you, and Ipresumed you had been told to watch out. If you had, the fire might nothave occurred. There must have been some error in Washington. But letme tell you now, Tom Swift--be on your guard!"