“But what do you expect to find?” Cub inquired.

“I don’t expect to find anything.  I had no expectation when I suggested that you boys canvass the radio field for information to clear up what you chose to call a mystery.  I had no idea what might turn up as a result of such canvass, but I know it was about the only thing for you to do to start a move in the desired direction.”

“And something sure did move,” Hal remarked appreciatively.

“Well, let’s run around this island and find a landing place,” Cub proposed.

The run was made, with Cub in charge of the wheel and engine controls.  They circumnavigated the island with unsatisfactory result.

“That settles it,” Bud declared.  “If San Salvador had been like that, Columbus would have made his first landing somewhere else!”

“Robinson Crusoe would never have found any footprints in the sand there,” Hal declared.

“Yes, we’ll give it up for the time being,” Mr. Perry declared.  “We won’t try to scale any perpendicular banks, fifteen or twenty feet high, at least, not to begin with.”

“I tell you what we ought to do,” Hal volunteered next.  “Let’s accept this island as the center of probability.”

“What in thunder is that?” Cub demanded.

“That’s a good one on you, son,” laughed the latter’s father.  “I thought you were the highbrow of your bunch; but here’s our subtle Tee-hee putting a bit of clever phraseology over on you.”

“Oh, I know what he means,” Cub rejoined with a panicky haste to recover lost prestige.  “I was just giving him a dig.  He’s forever giving me one, whenever I come along with anything of that kind.”

“It indicates that his mind is maturing rapidly,” said Mr. Perry.  “All right, Hal, we’ll accept this island as a center of probability—­what next?”

“Why, let’s cruise around about half a mile in all directions and pick out those islands that look as if they might have concealed a prisoner from view of passing boats.”

“That’s a good suggestion,” said Mr. Perry.  “Bob, start the boat again.”

The inspection required about an hour, at the end of which they compared notes and found that their island inventory disclosed the following conditions: 

Three possible places of concealment for the “Canadian Crusoe” had been discovered.  Two were small islands a short distance from each other in a region of shallows and more or less hidden by rows of long slim islands.  No boat of greater draught than a canoe could make its way through the intervening passages.  In other words, these islands were virtually isolated from all river traffic.  The other possible place of concealment was an island about five acres in extent, completely hemmed in by a group of other islands, which were so overrun with rampant vegetation, including bushes and trees, as to conceal the inner isle from any but the most scrutinizing vision.