The day had been very mild, with a gentle breeze sweeping to the northward and westward.  Toward the close of the day the sea-breeze died away, and hot, sultry breathings came from the great, sunburnt desert of Sahara.

Half an hour before sundown, the captain gave the cheering order to call the hands to “go in swimming”; and, in less than five minutes, the forms of our sailors were seen leaping from the arms of the lower yards into the water.

One of the sails, with its corners fastened from the main yard-arm and the swinging boom, had been lowered into the water, and into this most of the swimmers made their way.

Among those who seemed to be enjoying the sport most heartily were two boys, one of whom was the son of our old gunner; and, in a laughing mood, they started out from the sail on a race.

There was a loud ringing shout of joy on their lips as they put off; they darted through the water like fishes.  The surface of the sea was smooth as glass, though its bosom rose in long, heavy swells that set in from the ocean.

One of the buoys which was attached to the anchor, to show where it lay, was far away on the starboard quarter, where it rose and fell with the lazy swell of the waves.

Towards this buoy the two lads made their way, the old gunner’s son taking the lead; but, when they were within about sixty yards of the buoy, the other boy shot ahead and promised to win the race.

The old gunner had watched the progress of his son with great pride; and when he saw him drop behind, he leaped upon the quarter-deck, and was just upon the point of urging him on by a shout, when a cry was heard that struck him with instant horror.

“A shark! a shark!” shouted the officer of the deck; and, at the sound of those terrible words, the men who were in the water, leaped and plunged toward the ship.

Three or four hundred yards away, the back of a monster shark was seen cleaving the water.  Its course was for the boys.

For a moment the gunner stood like one who had lost his reason; then he shouted at the top of his voice for the boys to turn; but they heard him not.

Stoutly the two swimmers strove, knowing nothing of the danger from the shark.  Their merry laughter still rang over the waters, as they were both nearing the buoy.

O, what anxiety filled the heart of the gunner!  A boat had put off, but he knew it could not reach the boys in time to prevent the shark from overtaking them.

Every moment he expected to see the monster sink from sight,—­then he knew all hope would be gone.  At this moment a cry was heard on board the ship, that reached every heart,—­the boys had discovered their enemy.

The cry startled the old gunner, and, quicker than thought, he sprung from the quarter-deck.  The guns were all loaded and shotted, fore and aft, and none knew their temper better than he.

With steady hand, made strong by sudden hope, the old gunner pricked the cartridge of one of the quarter guns; then he took from his pocket a percussion cap, fixed it on its place, and set back the hammer of the gun-lock.