With the thought in mind that only the trail would be kept under watch by the Dyaks, he made up his mind he could readily contrive a ladder-like platform to extend from the brink, whereby the distance to the nearest tree might be conveniently bridged to permit easy access to the jungle. Of creepers and extra bamboo poles he had laid in ample stock. For the lack of better employment, he began the construction of his bridge when their meager luncheon had been finished.
His mind, as he worked, spun schemes innumerable for the daily defeat of the natives. Aware that as long as the terrace could be held starvation and thirst would be their only unconquerable enemies, he entertained no end of plans for catching fish without bait and even trapping or fishing up small animals that might rove at night below the cliff. From these reflections he returned to the men who prowled about them after dark.
To secure his cord across the trail and thereby provide an alarm, or notice of the enemy's approach, from that direction, was a very simple matter. When he finally invented, in his mind, a singular "rattle" to guard the approach by the cliff, he dropped all employment on the bridge at once and began forthwith on the other.
What he made was a series of bamboo buckets, or cuplike sections of the hollow tube, with stones suspended inside to knock against the walls when the things were lightly shaken. These he intended to hang, one beside another, in a line from the brink of the wall, where a climber must strike them unawares and sound a resonant warning.
But he found, on hanging a pair some ten feet down along the face, where the man had climbed in the night, that the wind would sway them to and fro against the rock and constantly ring their hollow tones.
This defect he presently remedied by forming a frame, some ten feet long and one foot wide, in which all his cups were suspended, or moored, both top and bottom. They were thus so lightly hung that the smallest jar against the frame would joggle them all to musical utterance, while the wind could have no effect on any single one.
The entire frame was lowered down till it rested a bit unevenly on two projecting shelves of rock, where it leaned a trifle outward like a picture on a wall, as the creepers that held it from falling were finally made secure. When Grenville, by way of a trial, nudged it once with a pole thrust down against it for the purpose, it rattled out a decisive alarm that one could have heard from the trail.