"Wait until I look at it," suggested Tom, as he opened one. His trained eye and touch soon told him that this explosive had not been tampered with.
"It's all right!" he shouted. "Into the gun with it, and we'll see what happens."
It was the work of only a few moments to put in the charge. Then, once more, the breech-block was slotted home, and the trailing electric wires unreeled to lead to the bomb-proof.
Tom Swift took one last look through the telescope sights of his giant cannon. He changed the range slightly by means of the hand and worm-screw gear, and then, with the others, ran to the shelter of the cave. For, though the gun had stood the previous tests well, Tom had used a heavier charge this time, both in the firing chamber and in the projectile, and he wanted to take no chances.
"All ready?" asked the young inventor, as he looked around at his friends gathered in the cave.
"I—I guess so," answered Ned, somewhat doubtfully.
Tom hesitated a moment, then, as his fingers stiffened to press the electric button there sounded to the ears of all a dull, booming sound.
"The dam! It has given way!" cried Ned.
