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.