"Well, it proved the accuracy of your aim, at any rate," observed Lieutenant Marbury."The bomb dropping device of your aerial warship is perfect--I can testify to that.""And I'll have the guns fixed soon, so there will be no danger of a recoil, 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 drop you in your own front yard, or even on your roof? I think I could manage that.""Bless my stovepipe, no, Tom! My wife would have hysterics.Just land me at Shopton and I'll take a car home."The damaged airship seemed little the worse for the test to which she had been subjected, and made her way at good speed in the direction of Tom's home.Several little experiments were tried on the way back.They all worked well, and the only two problems Tom had to solve were the taking care of the recoil from the guns and finding out why the propeller 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 up his 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 at something else.""No, Dad!" Tom cried."I'm going to make this work.I never had anything stump me yet, and I'm not going to begin now!""Well, that's a good spirit to show," said the aged inventor, with a shake 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 that seemed more simple.He knew that the gun question would take longer.
"Just what are you trying to find out, Tom?" asked Ned, a few nights later, when he found his chum looking at the broken parts of the propeller.
"Trying to discover what made this blade break up and splinter that way.It couldn't have been centrifugal force, for it wasn't strong enough."Tom was "poking" away amid splinters, and bits of broken wood, when he suddenly uttered an exclamation, and held up something."Look!" he cried."I believe I've found it.""What?" asked Ned.
"The thing that weakened the propeller.Look at this, and smell!" He held out a piece of wood toward Ned.The bank employee saw where a half-round hole had been bored in what remained of the blade, and from that 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 put in some sort of receptacle, or capsule, containing a corrosive acid.In due time, which happened to be when we took our first flight, the acid ate through whatever it was contained in, and then attacked the wood of the propeller blade.It weakened the wood so that the force used in whirling 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 havebeen killed."
"Yes, I know we might," said Tom."It must be the work of some of those foreign spies whose first plot we nipped in the bud.I must tell Marbury of this, but don't mention it to dad.""I won't," promised Ned.
Lieutenant Marbury agreed with Tom that someone had surreptitiously bored a small hole in the propeller blade, and had inserted a corrosive acid that would take many hours to operate.The hole had been varnished over, 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 nothing wrong.An effort was made to find out who had tried to destroy the Mars in midair, but it came to nothing.The two men in custody declared they knew 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 the problem of doing away with the gun recoil.He tried several schemes, and almost was on the point of giving up when suddenly he received a hint by reading an account of how the recoil was taken care of on some of the German Zeppelins.
The guns there were made double, with the extra barrel filled with water or sand, that could be shot out as was the regular charge.As both barrels were fired at the same time, and in opposite directions, with the same amount of powder, one neutralized the other, and the recoil was canceled, the ship remaining steady after fire.
"By Jove! I believe that will do the trick!" cried Tom."I'm going to tryit."
"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 managed it.Meanwhile, a careful watch was kept over the shops.Several new men applied for work, and some of them were suspicious enough in looks, but Tom took on no new hands.
Finally the new guns were made, and tried with the Mars held on the ground.They behaved perfectly, the shooting of sand or water from the dummy barrel neutralizing the shot from the service barrel.
"And now to see how it works in practice!" cried Tom one day."Are you with me for a long flight, Ned?""I sure am!"
The next evening the Mars, with a larger crew than before, and with Tom, 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 of the clouds, going on almost as naturally as though the occupants of the cabins were on the earth.Excellent meals were served.
"But when are you going to try the guns?" asked Ned, as he got ready to turn in.
"Tell you in the morning," replied Tom, with a smile.
And, in the morning, when Ned looked down through the plate glass in the 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 head straight for the Atlantic.Now we'll have a test with service charges andprojectiles!"
