of a sudden there was a loud cry of "man overboard!" and Jack saw the boy just going down in the water.

He was on the lower deck in a moment, and in another had thrown aside his coat and kicked off his shoes, running to the rail as he did so.

The cook had just been killing chickens on the forward deck, and was going aft with two or three fowls in one hand, a knife in the other.

As Jack reached the rail he saw something out on the water, just where the boy had gone down that made him turn icy cold in a moment.

Snatching the knife from the cook's hand, he sprang to the rail and leaped overboard, taking neither rope nor life preserver with him.

"By George! that's just what Jack feared, and there he is going to the rescue before any one has shouted, almost!" exclaimed Percival, as he hurried below.

"H'm! pretty clever of Sheldon," sneered a stout, unprepossessing boy, who seemed to be always scowling. "Knocks the kid overboard, and then goes to his rescue to make himself solid with the father. Very clever stroke, that, and just like him!"

"If you say anything like that of Jack Sheldon, Pete Herring," stormed Dick, who had heard the ill-natured remark, "I'll knock you overboard!"

Herring, who was by no means a favorite in the Academy, quite the reverse, in fact, had not supposed that Percival had heard his uncalled for and utterly false assertion, and now hurried away with a snarl, evidently fearing that Dick would carry out his threat.

The captain, as soon as possible, gave orders to stop the engines, and to hold the yacht near to the place where the boys had gone down, being ready to turn and go to their assistance when they should appear again.

All was excitement on board, for, until now, nothing had happened out of the ordinary, and no one thought of being seasick or of complaining of the monotony of the voyage.

Jack came to the surface, looked around him, saw young Jesse W. just coming up and shouting for help while he swam, and then, not far behind, what had caused him to take the knife with him, the sharp dorsal fin of a good-sized shark moving rapidly through the water.

CHAPTER II

JACK'S DARING RESCUE

Straight toward the swimming boy swam Jack, rapidly estimating the distance between them and the distance to be covered by the shark, the presence of which was not yet known by the younger boy.

He could swim, but he was more or less encumbered by his clothes, wide bottomed trousers and full shirt, and could not make as good progress as Jack in any event.

Then, as he was only a little fellow, and probably not accustomed to swimming very far out of his depth, Jack looked for his strength giving out at any moment.

"Keep up, J.W., you are doing fine!" he shouted, swimming straight on with a long, even stroke, which carried him rapidly toward the struggling boy.

Then some one on the yacht, with more anxiety than good judgment, shouted out so that all could hear him:

"Look out for the shark, look out!"

The instant that the younger boy heard this, he turned his head and cast a frightened look behind him, seeing the sharp fin just beginning to turn over in the water.

"Don't look, Jesse W., don't look, swim straight ahead!" cried Jack, who had come up with the boy.

Then he dove deep down so as to come up under the shark before he could turn and rush at the boy so near him.

Down went Jack, and presently began to rise, seeing the white belly of the man eater just above him.

With a fierce upward thrust of his right arm, which held the knife he had taken from the cook, he plunged the blade into the creature's vitals, drawing it downward and toward him, and turning his hand as he drew, thus making a jagged cut, and fairly laying open the shark's belly.

Young Smith, encouraged by Jack's shout, had darted ahead with his little remaining strength, not again looking back, and knowing too well what was about to happen when Jack dove.

As the shark, mortally wounded, floated away, to be eaten by others of his kind, Jesse W. suddenly became faint and felt himself giving out.

Jack arose in a moment, however, and called out cheerily:

"Hold on a moment, young fellow, and I'll be there. You mustn't give out yet, because they haven't put about to take us aboard."

The younger boy held out till Jack reached him, but seemed about to go under again when Jack said quickly:

"Here, get on my back and you won't have to swim. I'll tow you all right, and you can get rested."

"Did you kill him, Jack?" gasped the younger boy, as he obeyed the older one's instructions.

"Yes, yes, but never mind about that. Don't look behind you, just look straight ahead. I don't know that there's anything there anyhow, but it is always a good plan to look the way you're going to avoid accidents."

"You're a funny fellow, Jack," said the other. "You don't want me to see the sharks and be frightened."

"That's all right, old man, but there are no sharks at present, and if any come they will be too busy taking bites out of the other to bother me for a time. H'm! they are putting about. That's all right."

"You can carry me and swim yourself all right, Jack?" asked Jesse W. "Maybe I can swim a bit myself now."

"Never you mind about that," said Jack. "You just stay on my back till I tell you to get off," and the boy swam with a good, steady stroke toward the approaching yacht, keeping a lookout for sharks, as he knew they would be sure to appear soon, seeming to scent blood for miles.

Without letting the younger boy know that he was on the lookout he kept a strict watch on all sides for more of the rapacious creatures, and at length discovered two making for him in different directions, one of them suddenly appearing between him and the yacht, which was rapidly approaching.

"That fellow will be frightened off or perhaps go under the vessel," he thought, "but the other one is coming on pretty fast. I hope he won't get to the yacht before me."

The people on the yacht saw the shark between them and Jack, and Dick Percival seized a gun from the captain, aimed at the creature and fired, doing no great damage, but causing the voracious monster to rush off to one side, and out of his direct course.

Sharks have other fish to guide them, and without these they are helpless, which was the case with this one, who, in his sudden change of course, got away from his pilots, and had to be hunted up by them before he could get his bearings on the boys in the water.

This created a diversion in Jack's favor, and he swam on sturdily, splashing and kicking, and making a great disturbance to frighten away the second shark, which was coming alarmingly close to him.

The yacht was coming on, however, and now they bore down toward him, slackening speed a bit, one of the sailors throwing the boy a line.

Jack caught it with one hand, as it settled over his head, and said to the boy on his back:

"Hang on, young fellow, and they'll haul us both up together. You are no sort of weight, but just hang on."

Jesse W. did as he was told, and both boys were hauled on board the yacht, Dick, Harry, Arthur, Billy Manners and half a dozen others pulling in heartily on the line.

They were drawn on board just in time, for the baffled shark made one terrific jump out of water as they reached the deck, the gangway having been opened, and banged his nose against the plankshire, falling back into the sea with a great splash.

Bucephalus was at the gangway, an axe in his hand, and as the shark gave his jump he aimed a swinging blow at the monster, but failed to hit him.

"Go back dere, yo' sassy feller," he sputtered. "Ah jus' like to get one good crack at yo' an' Ah rip yo' side open. Don' yo' perambulate dis yer way again if yo' know what am salubrious fo' yo', yo'heah?"

Bucephalus was fond of using big words, but did not always use