Jack looked from the observation windows in the conning tower and saw, about a mile away a big steamer. From her side a white cloud of smoke floated, and then the water splashed about fifty feet from the blunt nose of the submarine.
Once more came the boom, the white cloud of smoke and this time the water splashed only twenty-five feet away from the bow of the Porpoise. A third time came the sound, and the splash was even nearer.
"They're firing on us!" yelled Jack.
At his cry the professor ran on deck. He was just in time to see the fourth shot made, and this time the shell dropped into the water just astern of the Porpoise and so close that when it exploded it sent a shower of spray all over the deck.
"Here! Stop that!" yelled Mr. Henderson, shaking his fist in the direction of the steamer. "You nearly hit us that time. Do your practicing in some other direction!"
"I don't think they can hear you," said Jack. "And besides, I don't believe they are practicing."
"Then what in the world are they doing?"
"Shooting at us I guess."
"Why do they want to shoot at us? We haven't done them any damage."
"Perhaps they think we are a torpedo boat," suggested Jack. "Maybe that vessel's nation is at war with some other one and wants to sink us if it can."