“Ah, bah!  They have gone foraging,” said Rodier, unwittingly hitting on the truth.

“But they would never leave the place unguarded,” replied Smith.  “The savages certainly attacked them; look at the arrows and spears.  But Mr. Underhill would not have yielded without fighting; yet there are no dead bodies, not even the cut-up earth there would be if they had had a tussle.  I can’t account for it any way.”

“Well, mister, we better look them up.”

“In the aeroplane, you mean?”

“Yes.  They must be here, in this island, or not here.  In the aeroplane we search all over.”

“It will be like looking for rabbits in bracken,” said Smith, pointing to the forest.  “Still, we must try.”

He sat down on a biscuit tin to think over the position and evolve a plan.  A random search might be mere waste of time.  Starting with the assumption that the castaways were still on the island, he said to himself that they must have left the fort voluntarily, or there would certainly be signs of a struggle.  That they had left no one on guard seemed to show that they were in no alarm, otherwise they would have carried their belongings with them.  His father, he knew, would not abandon his note-books and specimens.  Was it possible that they were making reprisals on the enemy who had previously attacked them?  But even in this case they would hardly have left their fort wholly undefended, unless in the heat of victory they had rushed out in headlong pursuit, a rash movement which a naval officer would hardly countenance.  Besides, they were but ill-provided with arms.  Had they been enticed forth by the savages?  In that case the savages would surely have plundered the camp, unless—­and now his thought and his pulse quickened—­unless there had not yet been time.  Perhaps they had only recently left the place.  Then they could not be far away, and if they had yielded to allurement there might still be time to save them.  He started up, and told Rodier, who had begun his customary task of cleaning the engine, the conclusion to which he had come.

“We will ascend at once,” he said, “and scour the neighbourhood.  The forest is thick, but perhaps there are clear spaces in it.  Let us lose no time.”

They dragged the aeroplane to the inner extremity of the enclosure, turned it round, and started it towards the sea.  In less than a minute it was two hundred feet in the air.  Then Smith wheeled round and steered across the camp, intending to take that as a centre, and strike out along successive radii, so that in the course of an hour or two, even at moderate speed, he would have searched a considerable extent of country in the shape of a fan.  It was a question how far he should proceed in one direction, but relying on his idea that the evacuation of the camp could only recently have taken place, he resolved to content himself at first with a distance of about ten miles.