d, promptly set out on an exploring expedition returning however
without incident at nightfall.

"Well," began the professor that evening when they had gathered on the
deck awaiting the supper call, "what did you find out about the island
to-day?"

"Not much of importance," replied Jim, "except that it is of very
considerable extent, very rugged and mountainous."

"But Jo had an awful scare," broke in Tom.

"You mean you did," protested Jo.

"How was that?" asked the professor.

"Why, we found a cave with the entrance way up in the air. We thought at
once that it was the one we were looking for, but it did not turn out to
be," explained Tom. "And then we found a lot of skeletons in there, and
they got after us."

"The skeletons did?"

"Well, something did," replied Tom with a grin. "Then Jo and I beat a
hasty retreat."

"Each got hold of the other in the dark," explained Jim, laughing, "but
I guess they had a jolly time of it till they broke away and ran. It
sure was funny."

"Are you certain there wasn't anything unnatural in there?"

"We couldn't find anything alive except some bats, when we went back,"
replied Tom, "although we hunted all over."

"What kind of a place is it?"

"The cave?"

"No, the island."

"It seems to be an uninhabited island as far as we could see," answered
Jim.

"Didn't you discover any signs of people at all?"

"Yes," replied Jim. "The same sign we saw from this deck. The smoke
signal."

"That cave will bear further investigation. It is certainly very
curious," mused the professor.

"What is?" queried Tom.

"About that smoke on the mountain."

"What do you think of it?" asked Jim.

"It is a signal of some kind, but if the island is uninhabited, who
could have made it?"

"Why couldn't the ones who made it come from some other island?" asked
Jim.

"And gone back again," suggested Jo.

"Perhaps so," replied the professor, "but that doesn't make it any
clearer."

"You never can see through smoke very well," suggested Jo.

"True," laughed the professor, "but still somehow I don't like it."

"Then we saw a ship in the distance, apparently headed for this island,
but far off the southern shore."

"Six o'clock," broke in Tom, as four bells were struck. "I think I will
accept the invitation to dine."

"A good plan," commended the professor, "and Monday we must get an early
start and learn, if we can about that ship you saw, and begin a more
thorough explorati