The whale turned and made a rush in the opposite direction to that of the divers. This was a welcome sign to the professor, for he knew the animal was seeking open water and this told him it must be somewhere in the vicinity.
Their hearts still beating loudly from the closeness of death, the adventurers continued their way. On every side were fish, big and little, and, though some of the larger ones thrust themselves to the men and boys, as if wondering what strange creatures they were, none of them offered to attack.
Led by the professor they made a complete circuit of the ship that was held fast in the ice. As the inventor had surmised, the Porpoise was nipped only above and below. If she could be freed at either of those points she could rise to the surface, or sink down under the ice.
After making a careful examination of the position of the craft, Mr. Henderson motioned to have the dynamite placed on the ice, in front of, and about two hundred feet away from the nose of the ship.
He connected the cartridges with the fuse and wires that were to explode them, and then, taking the free end, he started back toward the ship. Washington was on the watch for them, and operated the diving chamber. Soon the four were back in the Porpoise.
"Now to see if our plan will work," said Mr. Henderson. "I am relying on the well known downward force of dynamite to blow a hole in the bottom part of the ice, so that we can drop below."
"Why not make a hole above so we can rise and escape?" asked Bill.
"Because," replied the professor, "we are now in the region of perpetual ice. The ocean above us is one fast floe, or a number of smaller ones, so that, in any event our progress would be impossible. But we can sail far enough down under water to escape all the ice. That is the purpose of the Porpoise. That is why I built her. We will now begin on the last part of our voyage; that is if we can get free of the fearful grip of this sea of ice."
There was little they could do to protect themselves. They would either escape or be blown to pieces in case the explosive exerted too great a force. They all put on life preservers to guard against the contingency of the Porpoise being ripped apart and themselves cast into the water, yet they realized that without their ship, they could live but a little while in the ice-filled water near the south pole.
The professor saw that everything was in readiness. He hesitated a moment and looked at the electric button in his hand, for this time the dynamite was to be detonated by a battery. How much might depend on one push of the finger!