appearance, struggling terribly, and looking badly frightened.

There had been a time when Nick could not swim a stroke; but, by
keeping heroically at it, he had managed to master the art to some
extent. Desperation assisted him in this predicament, and the way he
threshed the water was a caution. Herb afterwards declared it beat any
old stern-wheel towboat he had ever seen, charging up the current of
the mighty Mississippi.

Luckily enough, Jack had anticipated something of this sort. That was
why he had persisted in keeping as close to the speed boat as he dared,
without risking a collision. He later on said he felt it in his bones
that if the _Wireless_ had one more kink of evil in her, she was just
bound to let it out at the most critical moment. And it had proven
just so.

The first thing Jack did when he saw the head and wildly plunging arms
of his fat chum appear, was to hurl the life preserver he had snatched
up from the spot where he kept it handy.

And so well aimed was the cork buoy that it fell just in front of the
struggling Nick, who gave a half-strangled whoop, doubtless under the
impression that it was a shark, or perhaps one of those same mermaids
he had declared it his ambition to meet face to face.

"Grab hold of it, Nick!" shouted George, excitedly.

"It's a life preserver. Get a grip on it, Nick!" bellowed Jack, as he
gradually turned the nose of the _Tramp_ around, meaning to bear down
upon the imperiled boy.

Luckily Nick heard what they said, for he was seen to make a wild
clutch for the floating buoy, and catch hold of it before the
treacherous swirls carried it beyond his reach.

"Oh! look there!" shrieked Jimmy. "That must be the fin of a shark!"

It was.

And further along Jack even caught sight of several more. The fierce
creatures had heard the splash, and apparently scenting a fine dinner,
were dashing this way and that, bent upon finding the object that had
made all the rumpus.

"George, get your gun, and be ready to shoot!" said Jack, himself pale
now with sudden anxiety.

So the skipper of the _Wireless_, understanding that this was a time to
keep cool if they would save their cheery comrade, reached down under
the side of his boat. When he bobbed up a few seconds later he was
clutching his rifle, which he had brought along, in the faint hope that
before the long cruise was done he might get a deer, or even a bear,
with it.

Now the nose of the _Tramp_ was he