wing way over to one side, or it may move only a short distance. That
represents intensity. If either you or George had sung that note I
should have been able to detect it, whatever its pitch or intensity,
because your voices are as unlike as different musical instruments, and
that is character, or timbre, as the French call it."

CHAPTER III

THE HIDDEN MESSAGE

While the work of getting out the planking for the boat was going on,
and the plowing had now been resumed, since the new yoke of oxen were
fitted to do the work, the boys were not forgetful of the usual weekly
outing. They had several quite important things right at home which
needed looking into, if they wanted to solve some of the things on the
island. First, the cave, which they had twice attempted to explore; the
search for their lost boat, which had the strange rope and oars; and the
mystery of the flag and pole.

These things weighed heavily on their minds, because these happenings
were close at hand. But what made the greatest impression on the minds
of all was the finding of the _Investigator's_ lifeboat. It seemed
almost like a call to them from the interior. The impatience of the boys
was almost beyond restraint, at times.

"It does seem to me that we should not delay an hour in making some
effort to explore the direction the boat came from," was George's view
of the situation as they canvassed the subject.

"That is my idea, also, and I am not in favor of giving much more time
to hunting or other forms of recreation until we know how that boat came
to South River."

"Yes; I can appreciate how anxious you are," said the Professor, after
the boys had given their views. "What we are doing, however, is
essential from every point of view. We must prepare provisions, so that
we shall be able to know where we can get them in case of need. On the
other hand, weapons are necessary, which take time to construct. If,
however, it is thought advisable, we might make a trip of explorations
along the South River, beyond the falls, the time to be limited to a
week; but I have my doubts of the wisdom of such a course."

This suggestion appealed strongly to the boys, who were always keen for
anything which savored of adventure, and it was some time before the
boys could reconcile themselves to the saner and more business-like
course of completing the boat and making the trip by water.

The weather was beautiful, and vegetation was springing up in ab