“Hurrah!” the bays heard him shout.  “I give him one plumb in the eye!  A fine shot!  And we hit him besides with the boat.  I guess he’s a goner!”

“I’m afraid not,” muttered the professor.  “That was a bad blow we struck him, but I think it will only ruffle his temper.  We’ll have to look sharp now, boys.”

By this time the ship had rushed past the whale, but the boys, looking through a window in the rear of the tower could see the huge body.  Now the fountains of water which the whale spouted were tinged with red.

“He’s bleeding!” exclaimed the professor.  “I guess Andy hit him in a vital spot.”

“But not vital enough!” cried Mark.  “See!  He’s coming after us!”

And so it proved.  The whale, angered, and, probably half crazed by the pain of the bullet and the blow, was coursing after the ship, coming on with the speed of an express train.  Straight at the Mermaid he lunged his huge bulk.

“We must escape him!” cried Mr. Henderson.  “If he hits us he’ll send us to the bottom!”

He had made ready to slow up the Mermaid to see if it had sustained any damage from the impact with the whale, but when he saw the monster coming after the boat he knew the only safety lay in flight.

“Let us go up into the air and so escape him!” cried Jack, with sudden inspiration.

For an instant neither Mark nor the professor grasped what Jack meant.  Then, with an exclamation, the professor pulled forward the lever that generated the gas and set working the gravity neutralizer, which would enable the ship to rise.

Faster through the water went the Mermaid, and faster after her came the whale.  Above the hum of the engines was heard the hiss of the powerful gas.  The ship trembled more violently.

“We are rising!” exclaimed the professor, as he looked at a gage.

The boys could feel the craft lifting from the waves which clung to her as if they hated to lose her.  The boys knew the gas was beginning to operate.

“If it is not too late!” whispered Mark, half to himself.

For the monster of the seas was coming on, lashing the water to foam with his terrible flukes, and sending aloft a bloody spray.  His speed was awful.

Now he was but ten feet away from the fleeing craft—­ now but eight—­ now five!  Ten seconds more and the big head, like the blunt stern of a battle ship, forced forward by the tons of blubber, flesh, bone and fat behind it would strike the Mermaid and crush it like an egg shell.

Now if ever was the need for the Flying Mermaid to prove herself worthy of the name.  Now, if ever, was the time for her to leave the watery element and take to the lighter one.

And she did.  With a last tremble, as if to free herself from the hold of the waves, the gallant craft soared up into the air, leaving the water, which dripped from her keel like a fountain’s spray, and shooting aloft like a bird, escaped her terrible enemy which passed under her, so close that the lower part of the Flying Mermaid scraped the whale’s back.