Walking rapidly, they arrived at the edge of the burned area in half an hour.  Smoke was still rising from smouldering embers at various points in the burned area; but there was no danger to be feared, for everything inflammable about these embers had been consumed.  Even should the wind fan them into a flame again they could do no harm, for there was nothing for them to feed upon.  Along the entire edge of the burned area the fire crew had made sure there was a wide belt of ground in which no spark remained.  Thus, though these glowing embers might continue to smoulder for hours, they could do no harm.  The quantity of smoke arising was still considerable, but it did not shut off the vision as the dense clouds of smoke had done during the fire.  So the onlookers could get a fair idea of the extent of the blaze.

The blackened area on which they looked, they were relieved to find, was not of great width, though it stretched from the edge of the brook on one side almost to the mountain on the other.  Altogether, the fire had swept over not more than a hundred acres.  Had it not been for the presence of the two boys, it might easily have destroyed thousands of acres.  The fire had started in a cut-over tract just below the edge of the virgin timber.  Had the morning proved windy, instead of calm, the flames would have gone racing into the big timber, with the chances good for a disastrous crown-fire, when the flames would have gone leaping from tree top to tree top, utterly consuming the forest, as the previous fires had destroyed the timber on Old Ironsides.  A lucky combination of circumstances alone had prevented a holocaust.

Climbing upon a high rock, the forester searched for the point at which the fire had originated.  Prom his pocket he drew some powerful field-glasses, and again and again swept his vision over the farther edge of the burned area.  Presently he closed his glasses and leaped to the ground.

“Come on,” he said, and headed diagonally across the burned tract.

In a few minutes the three stood on the unburned forest floor on the farther side of the strip of black.

“We must get our aerial up at once, Lew,” said Charley.  “It’s been three-fourths of an hour since we talked to Willie.”

They glanced about, selected two suitable trees, and had the supporting wires attached to them in no time, with the aerial dangling aloft between the trees.  It took only a moment more to couple up the instruments.

“CBWC—­CBWC—­CBWC—­CBC,” rapped out Charley, as soon as the outfit was in readiness.

Almost instantly Willie replied to the signal.

“Any message for us from Oakdale?” inquired Charley.

“Not a word.  What are you doing?”

“We are investigating the cause of the fire.  Have moved our aerial down past the burned area.  Forester and Lew and I alone.  Fire crew on way back to Oakdale.”

“Have you found cause of fire?”