The hours dragged very heavily while Beresford was absent at his work. Forrester had nothing to do. He roamed about the cavern, talked a little to Wing Wu, looked in at Beresford occasionally; but during the greater part of the day he had only his thoughts to occupy him. But it happened one day, as he passed the spot where the spare bamboo poles were laid, that an idea flashed into his mind. It seemed fantastic, probably impracticable; but it might at least be attempted: anything was better than this stagnant life in death.
The success or failure of the scheme that had occurred to him depended on the accuracy of Beresford's theory that the dust formed by the action of the rays on the cavern roof protected the rock from further destruction. If this was correct, and the dust could be removed, exposing fresh surfaces, the piercing of the chimney could be accelerated far beyond its normal rate. With a sufficiently long pole the dust coating could be brought down during the intervals when the rays were shut off by the slab. Such a pole might be constructed from the bamboo rods.
A difficulty arose from the fact that the cavern was never dark. It was always pervaded by the dim green light emanating from the walls. But the rods were partially screened by the sentry-box, and Forrester thought that in the dead of night, when the priest was asleep, and the negritos more or less drowsy, he might succeed in purloining the bamboo, and carrying it into the passage beyond the inner cavern.
Without mentioning the matter to Beresford, he waited till all was quiet, then stole round the wall towards the rods, picked up as many as he could carry, and made his way undetected to the place determined on. Next night he removed a few more in the same way. Their disappearance had apparently not been noticed by the priest.
The following day was Beresford's turn of duty. In the early morning, after the new priest had arrived, Forrester told his companion what he had done.
"Fiat experimentum!" cried Beresford delightedly. "I will tell you the result to-night. But not a word to Wing Wu. One of these days Wen Shih may occupy the sentry-box, and the poor lad will blab everything."
As soon as he had completed the transmutation of the allotted number of plates, Beresford fitted two of the bamboo rods together telescopically, tied his coat by its sleeves to the end of the pole thus formed, and inserting this wad into the cavity, thoroughly scoured its roof. A considerable quantity of fine dust fell on to the slab and the floor around. He then raised the slab, allowing the rays to play on the roof for a longer time than when the leaden plates were sunk in the pit. This process he repeated again and again, heedless of his increasing weariness and a stupefying headache, until Forrester rushed in hurriedly to say that the priest, evidently surprised at his unusually prolonged absence, was coming towards the passage to seek its explanation. Beresford instantly untied his coat, donned it, while Forrester laid the pole in the recess; then, taking Forrester's arm, met the priest at the entrance, feigning a deeper exhaustion than he actually felt. The priests seldom entered the inner cavern; this man threw a casual glance around it, and followed the prisoners back to the outer cavern, suspecting nothing.
"It works!" Beresford whispered when he got to his customary place, and at once fell into a dead sleep.
Later on, he told Forrester that the experiment had succeeded beyond his hope.
"As nearly as I could measure with the pole," he said, "the cavity is lengthened by at least a foot. The rays act with tremendous rapidity. In a few days, unless we are much deeper than I think, we shall have cut a hole right through to the level of the Temple floor."