"Can you see anything of him, Ned?"

"Not a thing, Mr. Damon. Wait--hold on--no! It's only a bird," and the lad lowered the glasses with which he had been sweeping the sky. looking for his chum returning in his airship with the powder.

"He'd better hurry," murmured the foreman. "That dam can't last much longer. The water is rising fast. When it does go out it will go with a rush. Then good-bye to the village of Preston."

"Bless my insurance policy!" cried Mr. Damon. "Don't say such things, my friend."

"But they're true!" insisted the man. "You can see for yourself that the cracks in the dam are getting larger. It will be a big flood when it does come. And I'm not altogether sure that we're safe up here," he added, as he looked down the sides of the hill to where the creek was now rapidly becoming a raging torrent.

"Bless my hat-band!" gasped Mr. Damon. "You--you are getting on my nerves

"I don't want to be a calamity howler," went on the foreman; "but we've got to face this thing. We'd better get ready to vamoose if Tom Swift doesn't reach here in time to fire that shot--and he doesn't seem to be in sight."

Once more Ned swept the sky with his glasses. The roar of the water below them could be plainly heard now.

"I wish I could get hold of that rascally German," muttered the foreman. "I'd give him more than a piece of my mind. It will be his fault if the town is destroyed, for Tom's plan would have saved it. I wonder who he can be, anyhow?"

"Some spy," declared Ned. "We've been having trouble right along, you know, and this is part of the game. I have some suspicions, but Tom doesn't agree with me. Certainly the fellow, whatever his object, has made trouble enough this time."

"I should say so," agreed the foreman.

"Look, Ned!" cried Mr. Damon. "Is that a bird; or is it Tom?" and he pointed to a speck in the sky. Ned quickly focused his glasses on it.

"It's Tom!" he cried a second later. "It's Tom in the Humming Bird!"

"Thank Heaven for that!" exclaimed Mr. Damon, fervently, forgetting to bless anything on this occasion. "If only he can get here in time!"

"He's driving her to the limit!" cried Ned, still watching his chum through the glass. "He's coming!"

"He'll need to," murmured the foreman, grimly. "That dam can't last ten minutes more. Look at the people fleeing from the valley!"

He pointed to the north, and a confused mass of small black objects--men, women and children, doubtless, who had lingered in spite of the other warning--could be seen clambering up the sides of the valley.

"Is everything ready at the gun?" asked Mr. Damon.

"Everything," answered Ned, whom Tom had instructed in all the essentials. "As soon as he lands we'll jam in the powder, and fire the shot."

"I hope he doesn't land too hard, with all that explosive on board," murmured the foreman.

"Bless my checkerboard!" cried Mr. Damon. "Don't suggest such a thing."

"I guess we can trust Tom," spoke Ned.

They looked up. The distant throb of the monoplane's motor could now be heard above the roar of the swollen waters. Tom could be seen in his seat, and beside him, in the other, was a large package.

Nearer and nearer came the monoplane. It began to descend, very gently, for well Tom Swift knew the danger of hitting the ground too hard with the cargo he carried.

He described a circle in the air to check his speed. Then, gently as a bird, he made a landing not far from the gun, the craft running easily over one of the few level places on the side of the hill. Tom yanked on the brake, and the iron-shod pieces of wood dug into the ground, checking the progress of the monoplane on its bicycle wheels.

"Have you got it, Tom?" yelled Ned.

"I have," was the answer of the young inventor as he leaped from his seat.

"Is it good powder?" asked the foreman, anxiously.

"I don't know," spoke Tom. "I didn't have time to look. I just rushed up to where I had stored it, got some out and came back with the motor at full speed. Ran into an airpocket, too, and I thought it was all up with me when I began to fall. But I managed to get out of it. Say, we're going to have it nip and tuck here to save the village."

"That's what!" agreed the foreman, as he helped Koku take the cans of explosive.

"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.

"That's it!" shouted the foreman. "Fire!"

Tom pressed the button. Once again was that awful tremor of the earth--the racking shake--the terrific explosion and a shock that knocked a couple of the men down.

"All right!" shouted Tom. "The gun held together. It's safe to go out. We'll see what happened!"

They all rushed from the shelter of the cave. Before them was an awe-inspiring sight. A great wall of water was coming down the valley, from a large opening in the centre of the dam. It seemed to leap forward like a race horse.

Tom declared afterward that he saw his projectile strike the barrier that separated one valley from the other, but none of the others had eyes-sight as keen as this--and perhaps Tom was in error.

But there was no doubt that they all saw what followed. They heard a distant report as the great projectile burst. Then a wall of earth seemed to rise up in front of the advancing wall of water. High into the air great stones and masses of dirt were thrown.

"A good shot!" cried the foreman. "Just in the right place, Tom Swift!"

For a moment it was as though that wall of water hesitated, not deciding whether to continue on down the populated valley, or to swing over into the other gash where it could do comparatively little harm. It was a moment of suspense.

Then, as Tom's great shot had, by means of the exploding projectile, torn down the barrier, the water chose the more direct and shorter path. With a mighty roar, like a distant Niagara, it swept into the new channel the young inventor had made. Into the transverse valley it tumbled and tossed in muddy billows of foam, and only a small portion of the flood added itself to the already swollen creek.

The village of Preston had been saved by the shot from Tom's giant cannon.