The next instant the ship careened as something struck her a violent blow on the port side. Everyone almost toppled over from the force of the impact.
"Dar he goes agin!" cried Washington.
"We're attacked by a whale!" said the professor. "We must rise to the surface or it may damage the ship."
"If it's a whale I'd like to get a shot at it," put in Andy Sudds, from the foot of the companion ladder leading into the tower.
"I don't know that it is a whale," went on the inventor. "But it must be something very big and strong."
"It's a monster of some sort," put in Andy, "and I want a chance at him."
"It's too risky," murmured the professor. "We couldn't get down to bottom here, as the water is several miles deep, and the pressure would crush the Porpoise, strong as she is."
Once more came a terrible blow and the ship rocked in a swirl of foam beneath the waves. In quick succession two more fierce onslaughts were made by the unseen monster.
"We'll have to do something," muttered Andy.
"You're right," agreed the professor. "Our only chance is to rise to the surface, for I do not believe the creature will follow us there. Empty the tanks, Washington."