Mr.Berg is Suspicious
Not for long did the young inventor endeavor to break his way out of the water-ballast tank by striking the heavy sides of it.Tom realized that this was worse than useless.He listened intently, but could hear nothing.Even the retreating footsteps of Andy Foger were inaudible.
"This certainly is a pickle!" exclaimed Tom aloud."I can't understand how he ever got here.He must have traced us after we went to Shopton in the airship the last time.Then he sneaked in here.Probably he saw me enter, but how could he knew enough to work the worm gear and close the door? Andy has had some experience with machinery, though, and one of the vaults in the bank where his father is a director closed just like this tank.That's very likely how he learned about it.But I've got to do something else besides thinking of that sneak, Andy.I've got to get out of here.Let's see if I can work the gear from inside."Before he started, almost, Tom knew that it would be impossible.The tank was made to close from the interior of the submarine, and the heavy door, built to withstand the pressure of tons of water, could not be forced except by the proper means.
"No use trying that," concluded the lad, after a tiring attempt to force back the sliding door with his hands."I've got to call for help."He shouted until the vibrations in the confined space made his ears ring, and the mere exertion of raising his voice to the highest pitch made his heart beat quickly.Yet there came no response.He hardly expected that there would be any, for with his father and Mr.Sharp away, the engineer absent on an errand, and Mrs.Baggert in the house some distance off, there was no one to hear his calls for help, even if they had been capable of penetrating farther than the extent of the shed, where the under-water craft had been constructed.
"I've got to wait until some of them come out here," thought Tom."They'll be sure to release me and make a search.Then it will be easy enough to call to them and tell them where I am, once they are inside theshed.But--" He paused, for a horrible fear came over him."Suppose they should come--too late?" The tank was airtight.There was enough air in it to last for some time, but, sooner or later, it would no longer support life.Already, Tom thought, it seemed oppressive, though probably that was his imagination.
"I must get out!" he repeated frantically."I'll die in here soon."Again he tried to shove back the steel door.Then he repeated his cries until be was weary.No one answered him.He fancied once he could hear footsteps in the shed, and thought, perhaps, it was Andy, come back to gloat over him.Then Tom knew the red-haired coward would not dare venture back.We must do Andy the justice to say that he never realized that he was endangering Tom's life.The bully had no idea the tank was airtight when he closed it.He had seen Tom enter and a sudden whim came to him to revenge himself.
But that did not help the young inventor any.There was no doubt about it now--the air was becoming close.Tom had been imprisoned nearly two hours, and as he was a healthy, strong lad, he required plenty of oxygen.There was certainly less than there had been in the tank.His head began to buzz, and there was a ringing in his ears.
Once more he fell upon his knees, and his fingers sought the small projections of the gear on the inside of the door He could no more budge the mechanism than a child could open a burglar-proof vault.
"It's no use," he moaned, and he sprawled at full length on the floor of the tank, for there the air was purer.As he did so his fingers touched something.He started as they closed around the handle of a big monkey wrench.It was one he had brought into the place with him.Imbued with new hope be struck a match and lighted his lantern, which he had allowed to go out as it burned up too much of the oxygen.By the gleam of it he looked to see if there were any bolts or nuts he could loosen with the wrench, in order to slide the door back.It needed but a glance to show him the futility of this.
"It's no go," he murmured, and he let the wrench fall to the floor.There was a ringing, clanging sound, and as it smote his ears Tom sprang up with an exclamation.
"That's the thing!" he cried."I wonder I didn't think of it before.I can signal for help by pounding on the sides of the tank with the wrench.The blows will carry a good deal farther than my voice would." Every one knows how far the noise of a boiler shop, with hammers falling on steel plates, can be heard; much farther than can a human voice.
Tom began a lusty tattoo on the metal sides of the tank.At first he merely rattled out blow after blow, and then, as another thought came to him, he adopted a certain plan.Some time previous, when he and Mr.Sharp had planned their trip in the air, the two had adopted a code of signals.As it was difficult in a high wind to shout from one end of the airship to the other, the young inventor would sometimes pound on the pipe which ran from the pilot house of the Red Cloud to the engine-room.By a combination of numbers, simple messages could be conveyed.The code included a call for help.Forty-seven was the number, but there had never been any occasion to use it.
Tom remembered this now.At once he ceased his indiscriminate hammering, and began to beat out regularly-- one, two, three, four--then a pause, and seven blows would be given.Over and over again he rang out this number--forty seven--the call for help.
