meal, and several times, when Mark spoke to him, he did not reply.

"I wonder if he is worried about something, or is thinking of
something which seems to be concealed in the storeroom," the boy
thought.

But, after a while, the professor seemed to be more like himself. He
was busy over several maps and charts, and then announced the ship
would try air-sailing again for a while.

"We can make better time above than we can on the water," he said,
"and I am anxious to get to the mysterious island and learn what is in
store for us."

Perhaps if the professor had been able to look ahead, and see what was
soon going to happen, he would not have been so anxious for it to
occur.

It was shortly after dinner when, the gas container having been
filled, the ship rose in the air, and began sailing over the ocean,
about a mile up. The day was a fine one, and, as they were moving
south, it was constantly growing warmer. Down on the water, in fact,
it was quite hot, but in the air it was just right.

Like some immense bird the Mermaid went flying through the air. The
boys and the professor sat upon the deck in easy chairs. It was like
being on the top of some tall "sky-scraper" building which, by some
strange power, was being moved forward. Below them the ocean tumbled
in long, lazy swells.