And so it was, for after that Bill tied a chair in front of his bunk, and if he did get out in his sleep he stumbled against it and awoke before he had gone far.
Northward the Porpoise continued on her journey. She entered a vast field of ice, and only her ability to sink below the surface enabled her to get through it unharmed. There were few adventures going home. Once a big whale rammed the ship, as had happened on the going voyage, and several times they were surrounded by hordes of wild polar fish and walrusses, but there were no accidents, and in a couple of weeks the ship entered the temperate zone.
Then came lazy happy days of sailing through the tropical region. They landed at several islands and renewed their supply of food.
"I'm coming back this way some day," observed Mr. Henderson one afternoon as the ship was sailing along on top of the waves.
"What for?" asked Jack.
"To investigate that strange island with a big hole in the middle that seems to lead to the centre of the earth," was the answer. "I have a fancy we can explore that by means of a balloon. I'm going to try."
"Will you take us along?" asked the two boys.
"I'll see," replied the professor.
And later on he did take them on a trip, a thousand miles underground,—but that is another story to tell.
It was about a week later that the voyagers came within sight of Key West.