“Coming around to my logic?” queried Kruger. “I don’t know, and don’t see what good it will do us if it was.”
“Neither did I until you spoke as you did a little while ago. However, I started to wonder just how much weight it took to set off that valve. We know that our combined weights will; I think that yours alone would, but we don’t know whether mine would and if it did, how little could be placed on that part of the floor without starting the works.”
“If yours touches it off what good would any further knowledge be?”
“It is not necessary to place all one’s weight on one block, is it? It might be possible to place branches or logs on the floor so that we would…” Kruger was on his feet again; there was no need to finish the sentence. This time Dar led the way back up the tunnel, Kruger remaining several paces behind.
In due time the roar of steam showed that the trigger had been activated. Kruger stayed where he was, while Dar moved back toward him. The roar ceased; it was definitely Dar who had operated the valve. It was difficult to be sure of the precise position of the trigger block in the nearly dark passage. Dar moved back and forth until he had located the edge of the sensitive area to the last inch; then he spoke to his companion.
“Nils, if you will go back to the open space and find some rocks of various weights we’ll learn just how sensitive this thing is. I’ll stay here and mark the place.”
“Right.” Kruger saw what the little fellow had in mind and obeyed without comment or question. He was back in five minutes with an armload of lava boulders whose total weight approximated Dar’s fifty-five pounds, and the two proceeded to roll them one by one across the fatal line. Some minutes of alternate roaring and silence yielded evidence that the trigger was indeed operated by weight and that approximately fifteen pounds was required to open the valves. Further, the fifteen pounds could be applied at any point in the width of the corridor for a distance of at least ten feet. Merely spreading their weights would do no good, it seemed; as soon as the total reached the fifteen-pound limit the steam came on.
“We can still make a bridge right across the thing,” pointed out Dar when this conclusion was reached.
“It’s going to be a job,” was Kruger’s rather pessimistic reply. “Two knives will mean quite a lot of whittling.”
“If you can think of something else I will be glad to try it. If not I suggest we start work.” As was so often the case Dar’s words seemed too sensible to oppose and they returned to the sunlight to seek materials.
Unfortunately, Kruger had been right too. They had the two knives, neither one particularly heavy. The trees of Abyormen differ among themselves as widely as those of any other planet, but none of them is soft enough to be felled with a sheath-knife in half an hour — or half a day. The travelers hoped to find something thick enough to carry them without bending noticeably and thin enough to cut and transport. The patch of forest in the crater was not very extensive, and they might have to be satisfied with much less than they wanted; neither could remember noticing a really ideal trunk during their earlier search, though of course they had had other matters in mind at the time.
Kruger was still dubious as they wandered about the crater floor. He was no lazier than the average, but the thought of attacking even a six-inch trunk with his knife did not appeal to him. That situation has probably been responsible for most of the discoveries and inventions of the last half million years, so it is not too surprising that his mind was busy with other things as they hunted.
Nor is it surprising that some facts which had been available in the filing-case of his mind for some time should suddenly fall together; that seems to be the way ideas are usually born.
“Say, Dar,” he said suddenly, “how come if this city is deserted, and the power plants presumably shut down, there is still all this steam? I can understand a simple lever-and-valve arrangement’s lasting this long, but what about the energy supply?”
“There is much steam around,” pointed out Dar. “Might they not have gone far underground, to tap the same fire that fed these volcanoes or the hot water at the village?” Kruger’s face fell a little, as he realized he should have thought of this himself.
“Just the same,” he said, “it seems to me that there can be only so much steam there. Why shouldn’t we leave some rocks on that trigger and just wait for the thing to run out?”
“It’s been running, on and off, for quite a while now,” said Dar doubtfully, “and hasn’t shown any signs of running down. Still, I suppose there’s a chance. Anyway, once the weight is in place it won’t use any of our time; we can go back to this job. Let’s do it.”
“It won’t take both of us. I’ll be right back.” Kruger returned to the tunnel, rolled one of the rocks they had left on the floor toward the trap until his ears told him it had gone far enough, and was back with Dar in less than two minutes.
By the perversity of fortune the only tree that seemed usable for their purpose was located about as far from the tunnel as it could be. Complaining about it would do no good, however, and the two set to work with their tiny blades. Its wood was softer than pine, but even so the seven-inch trunk took some time to cut through in the circumstances. They rested several times, and stopped to hunt and eat once, before the big plant came down.
This particular tree arranged its branches in more or less the fashion of a multi-layered umbrella, with four or five feet between layers. The plan was to save some of the branches from the layer nearest the base and from that nearest the top, so that they could serve as “legs” to keep the weight of the main trunk and its burdens off the ground. Kruger would not have been too surprised had the job taken a year, but determination and increasing skill paid their dividends and only a few terrestrial days passed before the work was ready to be dragged to the tunnel. Throughout that time the howl of the steam never subsided; there was no need to visit the tunnel to check the jets’ behavior. If there was any diminution in the sound it was too gradual for either of them to detect while they worked; the phenomenon that did attract their attention was its sudden stopping.
This happened just as they were starting to drag the log toward the tunnel. For a moment the echoes of the whistling roar played back and forth across the pit; then silence took their place. Dar and Kruger looked at each other for a moment, then, without pausing for discussion, started running toward the opening.
Dar reached it first in spite of his shorter legs; the undergrowth barring the way was sufficiently open to let him through fairly easily while Kruger had to force his way. The floor of the tunnel was wet with a trickle of near- boiling water, evidently from steam which had condensed on the walls and roof during the past few dozen hours. The air in the passage was only saved from being unbreathable by the draft entering it from the pit; only a few yards of the corridor could be seen in the swirling fog. Step by step they advanced as the current drove the mist curtain before it, and presently they reached the stones that had been left near the trigger block. Dar would have continued, but Kruger restrained him with a word of caution.
“Let’s hold it a moment and see whether the rock I put on the trigger is still there. Maybe it got washed off by the stream; it wasn’t very heavy.” Dar privately felt that a fifteen-pound boulder would need something more powerful than the trickle in the tunnel to shift it, but stopped anyway. Only a few moments were needed to see that the rock was still in place; presumably the trigger was still depressed, and therefore the steam had been shut off by some other cause. A little uneasily, Kruger shifted his own weight forward until he was beside the rock. Nothing happened, and for several seconds the two looked thoughtfully at each other. The same possibilities were passing through their minds.
Neither knew the details of the valve system that controlled the steam. There might be any number of safety devices for shutting it off before complete exhaustion of the supply — devices which could be overridden by other triggers if a determined effort was made to escape through the corridor. The trouble was that the makers were not human and, as far as could be told, not members of Dar’s race either; there was simply no way of guessing what they might have considered logical design.
“I guess there’s only one way to find out, Dar. You’d better let me go first; I could probably stand a brief dose if the thing started up, but from what your Teachers have said there’s no telling what it would do to you.”
“That’s true, but my weight is less. Perhaps it would be better if I were to start.”
“What good will that do? If it doesn’t trip for you we still won’t know that it won’t for me. You just be set to come on the double if I make it.” Dar offered no further argument but helped his big companion make sure that the small amount of equipment he carried was securely fastened — neither one wanted to come back for anything that was dropped. With this accomplished Kruger wasted no more time; he set off up the tunnel as fast as his strength would allow.
Dar watched until he was sure that the boy was well past the steam jets; then he followed. He caught up with Kruger at the mouth of the tunnel, but the two did not stop until they were outside the building from which the
