here close observation had brought worth while
results.

While they were talking, the yacht had run into the inner harbor, and
here even with the fierce wind playing havoc in the tree tops and out at
sea, the high hills afforded good and safe shelter.

CHAPTER XVIII.

A MYSTERIOUS HAPPENING.

The barometer rose shortly and climbed up as rapidly as it had earlier
fallen. In a brief time the skies had cleared and the wind settled to a
steady breeze.

"It seems to me," said the professor, looking about him, "that it was a
difficult thing to get in here, but to get out is going to be a more
difficult one."

"It will be all right," replied the captain, "if Berwick will fix up
that old tea kettle of his and give us some steam." Then addressing the
engineer, "Can't you do this while we are in here?"

"Maybe I can," replied the engineer, "if there is no more of the devil's
handiwork. There would not be much the matter with the machinery, if
there was not somebody undoing things."

"The sailors will have few duties, now, and we will have a double watch
set over the engine room," said the captain.

The distance to shore was now so short that getting back and forth was a
simple task, and as security was so seemingly assured, permission was
given for any outside of those on duty, to land and rove about at will.

"As we have found the island, let's find the cave," suggested Jo, as
they were preparing for a trip ashore.

"Then we can go home," added Tom, who, however ready to venture forth,
was even more disposed toward the home journey. Whatever desire he may
have had toward early home going in this instance was destined by events
he could not forecast, to be blotted out.

"There is that column of smoke again," announced Jo, as he grasped the
oars. His brothers and Juarez were with him in the boat.

The others once more observed the curious signal, if such it were, but
gave no special heed other than to note its distance. On land, however,
they bent their footsteps in the direction of the phenomenon although
they could no longer see it for a guide.

They found themselves trailing off on a route they had not before taken,
and had gone perhaps half the distance which they had estimated as
required, when they came upon a curious clearing in the woods. It was
about forty yards in diameter, and surrounded by a complete circle of
trees, their boughs interlacing about seventy feet above to form a
lovely green cano