On came the whale. She was a huge, humpbacked monster, with a gigantic square head that looked as solid as the prow of a battleship. Every instant appeared to increase the speed at which she traveled. Fascinated by terror they could not take their eyes off the onrushing peril,—with the exception, that is, of Jack.

The boy was struggling with an auxiliary valve for gas supply which had been installed with the idea of quick-filling the bag. But the ordinary valve had worked so well alone that the auxiliary had not been used, and it was jammed and corroded.

“Hurry! hurry!” shouted Tom. “She’ll ram us in another second!”

But still the ship would not rise. The bag was swelling every instant, though, and it seemed that if they were granted only a molecule more of time there might be a possibility of rising before the whale struck them.

Among other things, the Wondership had been provided with conveniently placed life preservers. Jack now shouted to the others to put these on.

“When she hits, jump outwards!” he yelled.

They began to adjust the life saving contrivances, which laced on like jackets. But before they had them half ready the whale was within a few feet of the craft. Such was her speed that in front of her there was a mighty mass of blue water piled up. Her blunt, square forehead had raised the billow just as a round-bowed ship will “push the river in front of it,” to use a graphic sailor phrase.

And now an astonishing thing happened. The wave struck the frail motor ship a few seconds before the impact of the whale’s head. The great sea gave the craft just the impetus that was required. Buoyed up by the inflated gas-bag the wonder craft rose into the air as the wave rolled under her, and hung suspended in that element for some minutes. She did not rise far above the water, but the five or six feet that she reached was sufficient to clear the onrushing whale.

As the huge, humped back with its ugly rough hide passed under them Captain Sprowl picked up a rifle and pumped an unmerciful stream of lead into the monster.

Instantly she spouted, and the boys and their companions found themselves in the midst of a downpour of water and vapor. But the main danger had almost miraculously been avoided. As the Wondership settled down to the water once more, the whale could be seen rushing blindly on. A cheer went up from the boys.

“That’s the time we fooled her!” cried Tom exultantly.

But Captain Sprowl urged Jack to get the bag fully inflated as quickly as possible.

“She’ll be back afore long,” he prophesied. “She’s as mad as Pharaoh’s sow right now, and she won’t give up as easy as all that.”

Sure enough, in a few minutes the mound of water that marked the whale’s progress could be seen returning toward them at the same rapid speed. But by this time, Jack had secured a wrench and had managed to turn the stubborn auxiliary valve. As the whale neared them, he set the rising planes and started up the propeller.

The motor craft hesitated, and then like a wind-driven leaf she shot upward. It was not an instant too soon. As her rudder rose drippingly from the sea, the whale rushed viciously under her. Another fraction of a second and there would have been a different ending to this story.

“Saved, by the great horn spoon!” roared out Captain Sprowl. “Lad, that gas-meter thing of yours worked just in time.”

“It certainly did,” agreed Jack, ordering Tom to set the rising planes at a sharper angle.

“Look!” shouted Tom suddenly as they shot upward, soaring above the smooth surface of the ocean. “The sword-fish is going to attack the whale herself, now.”

They saw, far below them,............