"I will tell you what I believe," he said at length. "I have never
spoken of it before, but now that we are fairly started and may
eventually have a chance to prove my theory, I will say that I think
the centre of this earth on which we live is hollow. Inside of it,
forming a core, so to speak, I believe there is another earth, similar
to ours in some respects which revolves inside this larger sphere."

They were well out to sea now, as they could observe when they emerged
on the little deck. Above their heads was the aluminum gas holder,
which served as a sort of protection from the sun that was quite warm.
The Mermaid rode with an easy motion, being submerged just enough to
make her steady, yet not deep enough to encounter much resistance from
the water. In fact it could not have been arranged better for speed or
comfort.

"I think we will sail well to the eastward before making our course
south," Mr. Henderson said. "I do not care to meet too many ships, as
those aboard will be very curious and I do not want too much news of
this venture to get out. We will take an unfrequented route and avoid
delays by being hailed by every passing vessel whose captain will
wonder what queer craft he had met with."

The boys enjoyed the sail, for the weather could not have been better.
Even old Andy, who seldom said much, seemed delighted with the
prospect of having strange adventures. He had his rifle with him, and,
indeed, he seldom went anywhere that he did not carry it.

"For there's no telling when you may see something you want to shoot
or that ought to be shot," he used to say, "and it's always the man