Tom now went, cautiously feeling his way, to the extreme verge of the precipice, and, bidding his men keep silence, strained his ears to catch any sounds from below. There was not a murmur. He judged that the Arabs had hastily left their camp and made their way up to the south gate to meet the anticipated attack. It appeared safe.
The twenty Bahima began to dig a passage through the debris. Not a word was spoken. The din in the village was beginning to lull. Tom despatched Mbutu with the request that the noise should be kept up. The baskets of earth, as they were filled, were carried to the stockade and emptied on the inside. The work went on as rapidly as possible in the darkness, the men toiling with unabated zeal, sure that Kuboko, the man of big medicine, must have some excellent plan in view. Meanwhile the chief, finding the Arabs pressing close, and their rifle fire, erratic as it was, becoming dangerous, had withdrawn his sortie-party into the village; but the drums still maintained a tremendous din that must have been heard in the still night air for many miles.
Rather more than two hours had gone, and only the first part of the task Tom had in his mind was completed. A clear passage ten feet wide had been cut from the summit of the cliff into the cavern. Ordering the panting negroes to sit down and rest, Tom walked back the twelve feet to the stockade, took a string of bush-rope from his pocket, and tying it to one of the palings, returned to his men. The straight line made by the string lay in the direction of the tank. Then he set the men to dig a trench along the line towards the stockade, making it ten feet wide and three deep. He ordered them to stop within a foot of the fencing, lest that should be loosened by the movement of the earth. This took another two hours, as nearly as Tom could judge. It was approaching three o'clock in the morning, and there was still much to be done before his arrangements were complete. Thinking it wise to defer the rest of his operations, for which light was absolutely necessary, he dismissed the men, returned to the village, and sent word to the chief that the weary drummers might now take their well-earned rest.
Then he unfolded his scheme to the wondering chief. The Arab camp at the foot of the precipice was, it was true, secure from missiles hurled over the spur; but it was immediately below the cavern. Tom's plan was to let the water from the full reservoir suddenly into the cavern, and he calculated that the force it gained as it plunged thence over the precipice would be sufficient to work havoc below. The reservoir was eighty yards long and sixty wide; its depth was more than six feet; the weight of the water it contained was thus some seven thousand tons. By the time this immense quantity, gathering impetus as it fell, reached the camp two hundred feet beneath its outlet, the dynamic energy it would have acquired would be tremendous. The plan threw Barega into wild excitement, and he was eager to see it carried out at once; but Tom smilingly informed him that there was work still to be done, and, thanking him for so admirably making a noise, advised him to retire to his hut and finish his broken sleep.