He noticed that even during the few seconds in which he had been in communication with the yacht the situation had changed. One of the masts was now tenantless. Presumably its occupant had been washed off or through fatigue had dropped into the sea. But as the airship drew rapidly nearer, it was noticed that the figure on the other mast was bending low as if to raise something from the water. Then a head and shoulders appeared above the surface. Clearly the man Tom had supposed to be lost was trying to make his way to the mast to which his companion clung. The airship was now less than half a mile distant, and from the altitude to which they had risen—some three hundred feet above the surface—the occupants could see every detail in the strange drama that was being enacted beneath them. Assisted by the figure above, the swimmer was gradually making his way on to the mast, when suddenly a black fin appeared above the surface a few yards off. With a convulsive movement, the lowermost man had just succeeded in swinging himself a foot or two up the mast when the gaping jaws of a shark passed immediately beneath him. Tom shuddered involuntarily. The man had escaped by a few inches at the most. In a second the shark turned and glided beneath the clinging figure. The terror-stricken wretch clutched wildly at the man above him, and began to haul himself up hand over hand, clinging to his companion’s body. But the latter, unable to bear the double weight on the smooth mast, slipped slowly downwards. He was the slighter of the two, and no match, apparently, for the man who had usurped his place. “What a beast!” ejaculated Tom, wondering at this strange want of fellow-feeling in a man who was evidently older and stronger than his companion in distress. Slowing down, he fixed his eyes on the extraordinary spectacle. The position was now reversed. The younger and slighter man was very manifestly the under dog. With every attempt on his part to swarm up the mast the man above him kicked savagely, while the shark circled below. The fact that the second mast had become untenable seemed to indicate that the tide was rising. Neither of the men, their whole attention fixed on the sea beneath, had noticed the airship that was now hovering just above their heads.