Meanwhile Professor Henderson was trying to make up his mind what to do.  He wanted very much to get to the exact north pole, or the spot where the imaginary pole was supposed to be.  But he hesitated about taking the airship back over the course, and run the chance of again encountering the whirlwind.

“The more I think of it,” he said to Jack and Mark, who had joined him, “the more I think that the whirlwind is always there.  It did not come to us, we ran into it.  It may be caused by the magnetic currents at the pole eternally revolving.  I am afraid to go back within their influence, for it might mean death.”

“I have a plan,” said Jack modestly.

“Let us hear it,” came from the professor.  “I am at a loss what to do.”

“Supposing we let the ship down now,” Jack continued, “and walk back until we come to the north pole, since it must be near here.  We can take along the deflecting needle to tell when we reach it, and the whirlwind will not do much harm if we are on the ground and afoot.”

“Good idea!” exclaimed the professor.  “We’ll do it.  Washington, let the gas out and we’ll descend!”

In a few minutes a hissing told that the gas was being let out of the silk bag.  Soon the ship began to sink gently toward the earth, through the clouds of snow.

“Let us go outside,” suggested Jack.  “The wind doesn’t blow now, and the snow will not hurt us.  We will be warm enough in our furs.”

Mark voted the suggestion a good one, and the two boys went out on the deck.  Washington was busy in the engine room, and the professor was in the conning tower, so they did not go, but Tom and Bill said they would like to get a little fresh air, even if the temperature was far below zero, and they joined the lads.

The four stood and gazed in wonder at the strange scene.  At first the terrible cold cut them as if it was a keen knife.  But they soon grew used to it, and enjoyed what little of it reached them through the opening in their fur caps.  The snowflakes covered everything and the airship looked more like a craft bedecked from stem to stern with cotton batting than anything else.  Jack and Mark walked around to the stern.  Suddenly Mark stumbled over something.

“What’s this?” he cried.

Jack hurried to his side.  As he did so the bundle gave a heave, and, breaking through the snow blanket, there was displayed the calm features of Dirola.

“Me sleep!” she announced with a smile.

And that was what she had been doing while the airship was being whirled around by the strange force!  She had braced herself in a corner, pulled her furs about her face, and slumbered, even when the ship turned over.  So well braced was she that she did not tumble off.

“Well!  She’s a cool one!” exclaimed Mark.

“I guess you’d be too, if you slept out of doors with the temperature about seventy below zero,” remarked Jack.  “But let’s go in and tell the professor Dirola is here.  He may be worried about her.”