Chapter Five. 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 the shed. 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