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.