CHAPTER XVII
AN OCEAN FLIGHT
Dropping bombs from an aeroplane, or a dirigible balloon, is acomparatively simple matter. Of course there are complications that mayensue, from the danger of carrying high explosives in the limitedquarters of an airship, with its inflammable gasoline fuel, andever-present electric spark, to the possible premature explosion of thebomb itself. But they seem to be considered minor details now.
On the other hand, while it is comparatively easy to drop a bomb from amoving aeroplane, or dirigible balloon, it is another matter to makethe bomb fall just where it will do the most damage to the enemy. It isnot easy to gauge distances, high up in the air, and then, too,allowance must be made for the speed of the aircraft, theever-increasing velocity of a falling body, and the deflection causedby air currents.
The law of velocity governing falling bodies is well known. It varies,of course, according to the height, but in general a body fallingfreely toward the earth, as all high-school boys know, is acceleratedat the rate of thirty-two feet per second. This law has been takenadvantage of by the French in the present European war. The French dropfrom balloons, or aeroplanes, a steel dart about the size of a leadpencil, and sharpened in about the same manner. Dropping from a heightof a mile or so, that dart will acquire enough velocity to penetrate aman from his head all the way through his body to his feet.
But in dropping bombs from an airship the damage intended does not somuch depend on velocity. It is necessary to know how fast the bombfalls in order to know when to set the time fuse that will explode it;though some bombs will explode on concussion.
At aeroplane meets there are often bomb-dropping contests, and ballsfilled with a white powder (that will make a dust-cloud on falling, andso show where they strike) are used to demonstrate the birdman'saccuracy.
"We'll see how our bomb-release works," Tom went on. "But we'll have todescend a bit in order to watch the effect."
"You're not going to use real bombs, are you, Tom?" asked Ned.
"Indeed not. Just chalk-dust ones for practice. Now here is where thebombs will be placed," and he pointed to the three openings in thefloor of the amidship cabin. The wire nettings were taken out and onecould look down through the holes to the earth below, the ground beingnearer now, as Tom had let out some of the lifting gas.
"Here is the range-finder and the speed calculator," the young inventorwent on as he indicated the various instruments. "The operator sitshere, where he can tell when is the most favorable moment for releasingthe bomb."
Tom took his place before a complicated set of instruments, and beganmanipulating them. One of his assistants, under the direction ofLieutenant Marbury, placed in the three openings bombs, made of lightcardboard, just the size of a regular bomb, but filled with a whitepowder that would, on breaking, make a dust-cloud which could beobserved from the airship.
"I have first to determine where I want to drop the bomb," Tomexplained, "and then I have to get my distance from it on therange-finder. Next I have to know how fast I am traveling, and how farup in the air I am, to tell what the velocity of the falling bomb willattain at a certain time. This I can do by means of these instruments,some of which I have adapted from those used by the government," hesaid, with a nod to the officer.
"That's right--take all the information you can get," was the smilingresponse.
"We will now assume that the bombs are in place in the holes in thefloor of the cabin," Tom went on. "As I sit here I have before me threebuttons. They control the magnets that hold the bombs in place. If Ipress one of the buttons it breaks the electrical current, the magnetno longer has any attraction, and it releases the explosive. Now lookdown. I am going to try and drop a chalk bomb near that stone fence."
The Mars was then flying over a large field and a stone fence was inplain view.
"Here she goes!" cried Tom, as he made some rapid calculations from hisgauge instruments. There was a little click and the chalk bomb dropped.There was a plate glass floor in part of the cabin, and through thisthe progress of the pasteboard bomb could be observed.
"She'll never go anywhere near the fence!" declared Ned. "You let itdrop too soon, Tom!"
"Did I? You just watch. I had to allow for the momentum that would begiven the bomb by the forward motion of the balloon."
Hardly had Tom spoken than a puff of white was seen on the very top ofthe fence.
"There it goes?" cried the lieutenant. "You did the trick, Swift!"
"Yes, I thought I would. Well, that shows my gauges are correct,anyhow. Now we'll try the other two bombs."
In succession they were released from the bottom of the cabin, at otherdesignated objects. The second one was near a tree. It struck withinfive feet, which was considered good.
"And I'll let the last one down near that scarecrow in the field," saidTom, pointing to a ragged figure in the middle of a patch of corn.
Down went the cardboard bomb, and so good was the aim of the younginventor that the white dust arose in a cloud directly back of thescarecrow.
And then a queer thing happened. For the figure seemed to come to life,and Ned, who was watching through a telescope, saw a very much excitedfarmer looking up with an expression of the greatest wonder on hisface. He saw the balloon over his head, and shook his fist at it,evidently thinking he had had a narrow escape. But the pasteboard bombwas so light that, had it hit him, he would not have been injured,though he might have been well dusted.
"Why, that was a man! Bless my pocketbook!" cried Mr. Damon.
"I guess it was," agreed Tom. "I took it for a scarecrow."
"Well, it proved the accuracy of your aim, at any rate," observedLieutenant Marbury. "The bomb dropping device of your aerial warship isperfect--I can testify to that."
"And I'll have the guns fixed soon, so there will be no danger of arecoil, too," added Tom Swift, with a determined look on his face.
"What's next?" asked Mr. Damon, looking at his watch. "I really oughtto be home, Tom."
"We're going back now, and down. Are you sure you don't want me to dropyou in your own front yard, or even on your roof? I think I couldmanage that."
"Bless my stovepipe, no, Tom! My wife would have hysterics. Just landme at Shopton and I'll take a car home."
The damaged airship seemed little the worse for the test to which shehad been subjected, and made her way at good speed in the direction ofTom's home. Several little experiments were tried on the way back. Theyall worked well, and the only two problems Tom had to solve were thetaking care of the recoil from the guns and finding out why thepropeller had broken.
A safe landing was made, and the Mars once more put away in her hangar.Mr. Damon departed for his home, and Lieutenant Marbury again took uphis residence in the Swift household.
"Well, Tom, how did it go?" asked his father.
"Not so very well. Too much recoil from the guns."
"I was afraid so. You had better drop this line of work, and go atsomething else."
"No, Dad!" Tom cried. "I'm going to make this work. I never hadanything stump me yet, and I'm not going to begin now!"
"Well, that's a good spirit to show," said the aged inventor, with ashake of his head, "but I don't believe you'll succeed, Tom."
"Yes I will, Dad! You just wait."
Tom decided to begin on the problem of the propeller first, as thatseemed more simple. He knew that the gun question would take longer.
"Just what are you trying to find out, Tom?" asked Ned, a few nightslater, when he found his chum looking at the broken parts of thepropeller.
"Trying to discover what made this blade break up and splinter thatway. It couldn't have been centrifugal force, for it wasn't strongenough."
Tom was "poking" away amid splinters, and bits of broken wood, when hesuddenly uttered an exclamation, and held up something. "Look!" hecried. "I believe I've found it."
"What?" asked Ned.
"The thing that weakened the propeller. Look at this, and smell!" Heheld ou
t a piece of wood toward Ned. The bank employee saw where ahalf-round hole had been bored in what remained of the blade, and fromthat hole came a peculiar odor.
"It's some kind of acid," ventured Ned.
"That's it!" cried Tom. "Someone bored a hole in the propeller, and putin some sort of receptacle, or capsule, containing a corrosive acid. Indue time, which happened to be when we took our first flight, the acidate through whatever it was contained in, and then attacked the wood ofthe propeller blade. It weakened the wood so that the force used inwhirling it around broke it."
"Are you sure of that?" asked Ned.
"As sure as I am that I'm here! Now I know what caused the accident!"
"But who would play such a trick?" asked Ned. "We might all have beenkilled."
"Yes, I know we might," said Tom. "It must be the work of some of thoseforeign spies whose first plot we nipped in the bud. I must tellMarbury of this, but don't mention it to dad."
"I won't," promised Ned.
Lieutenant Marbury agreed with Tom that someone had surreptitiouslybored a small hole in the propeller blade, and had inserted a corrosiveacid that would take many hours to operate. The hole had been varnishedover, probably, so it would not show.
"And that means I've got to examine the other two blades," Tom said."They may be doctored too."
But they did not prove to be. A careful examination showed nothingwrong. An effort was made to find out who had tried to destroy the Marsin midair, but it came to nothing. The two men in custody declared theyknew nothing of it, and there was no way of proving that they did.
Meanwhile, the torn gas bag was repaired, and Tom began working on theproblem of doing away with the gun recoil. He tried several schemes,and almost was on the point of giving up when suddenly he received ahint by reading an account of how the recoil was taken care of on someof the German Zeppelins.
The guns there were made double, with the extra barrel filled withwater or sand, that could be shot out as was the regular charge. Asboth barrels were fired at the same time, and in opposite directions,with the same amount of powder, one neutralized the other, and therecoil was canceled, the ship remaining steady after fire.
"By Jove! I believe that will do the trick!" cried Tom. "I'm going totry it."
"Good luck to you!" cried Ned.
It was no easy matter to change all the guns of the Mars, and fit themwith double barrels. But by working day and night shifts Tom managedit. Meanwhile, a careful watch was kept over the shops. Several new menapplied for work, and some of them were suspicious enough in looks, butTom took on no new hands.
Finally the new guns were made, and tried with the Mars held on theground. They behaved perfectly, the shooting of sand or water from thedummy barrel neutralizing the shot from the service barrel.
"And now to see how it works in practice!" cried Tom one day. "Are youwith me for a long flight, Ned?"
"I sure am!"
The next evening the Mars, with a larger crew than before, and withTom, Ned, Mr. Damon and Lieutenant Marbury aboard, set sail.
"But why start at night?" asked Ned.
"You'll see in the morning," Tom answered.
The Mars flew slowly all night, life aboard her, at about the level ofthe clouds, going on almost as naturally as though the occupants of thecabins were on the earth. Excellent meals were served.
"But when are you going to try the guns?" asked Ned, as he got ready toturn in.
"Tell you in the morning," replied Tom, with a smile.
And, in the morning, when Ned looked down through the plate glass inthe cabin floor, he uttered a cry.
"Why, Tom! We're over the ocean!" he cried.
"I rather thought we'd be," was the calm reply. "I told George to headstraight for the Atlantic. Now we'll have a test with service chargesand projectiles!"
Tom Swift and His Aerial Warship; Or, The Naval Terror of the Seas Page 17