The next day every one was so busy that no one, not even Mark,
recalled the little excitement of the night before. Shortly after
noon, final preparations having been made, they all got aboard the
Mermaid and started off.

It was a bright sunshiny day, and the craft, speeding away from the
island where it had been constructed, over the dancing blue waves,
must have presented a strange sight had there been any spectators. For
surely no such ship had ever before sailed those waters.

However, there was no other vessel in sight, and the island, as far as
the professor and his friends knew, had never been inhabited.

"We will not try for any great speed," Mr. Henderson remarked as he,
with Mark and Jack, stood in the conning tower managing the Mermaid.
"We don't want to strain any joints at the start or heat any engine
bearings. There will be time enough for speed later."

"Yes, and we may need it more when we get into the centre of the earth
than we do now," observed Mark.

"Why so?" asked Jack.

"No telling what we may run up against underneath the ground," went on
Mark. "We may have to fight strange animals and stranger beings.
Besides, the atmosphere and water there can't be the same as up here;
do you think so, Professor?"

For a few minutes the scientist was silent. He seemed to be thinking
deeply.