Heavy Planet

scuffed the rocks under them backward; but he had forgotten the effect of the pneumatic mattress above. The truck had settled under its own weight and the downward thrust of the gas pressure until the chassis between the treads had met the bottom. Looking up, Beetchermarlf could see the bulge in the mattress where the entire drive unit had been let down some four inches. Takoorch appeared from his shelter and looked the situation over, but said nothing. There was nothing useful to say. Neither of them could guess how much more give there was to the mattress, and how much farther the truck would have to be let down before it would really hang free, though they knew the details of the Kwemb/y’s construction. The mattress was not a single gas bag but was divided into thirty separate cells, having two trucks in tandem attached to each. The helmsmen knew the details of the attachment-boch had just spent many hours repairing the assemblies — but even the recent display of the Kwembly’s underside with the weight off nearly all the trucks left them very doubtful about how far any one truck could extend by itself. “Well, back to stone lugging,” remarked Takoorch as he worked his nippers under a pebble. “Maybe these have been jarred loose now; otherwise it’s going to be awkward, getting at them only from the ends.”

“There isn’t enough time for the job. The ice is still growing toward us. We might have to get the treads a whole body-length deeper before they’ll run free. Leave the trucks alone, Tak. We’ll have to try something else.”

“All I want to know is what.” Beetchermarlf showed him. Taking a light with him this time, he climbed once more to the top of the truck. Takoorch followed, mystified. The younger sailor reared up against the shaft which formed the swiveling support of the truck, and attacked the mattress with his knife. “But you can’t hurt the ship!” Takoorch objected. “We can fix it later. I don’t like it any better than you do, and I’d gladly let the air out by the regular bleeder valve if we could only reach it; but we can’t, and if we don’t get the load off this truck very soon we won’t do it at all.” He continued slashing as he spoke. It was little easier than moving the stones. The mattress fabric was extremely thick and tough; to support the Kwembly it had to hold in a pressure more than a hundred pounds per square inch above the ground. One of the nuisances of the long trips was the need to pump the cells up manually or to bleed off excess pressure, when the height of the ground they were traversing changed more than a few feet. At the moment the mattress was a little flat, since no pumping had been done after the run down the river, but the inner pressure was that much higher. Again and again Beetchermarlf sliced at the same point on the tautstretched surface. Each time the blade went just a little deeper. Takoorch, convinced at last of the necessity, joined him. The second blade’s path crossed that of the first, the two flashing alternately in a rhythm almost too fast for a human eye to follow. A human witness, had one been possible, would have expected them to sever each other’s nippers at any moment. Even so, it took many minutes to get through. The first warning of success was a fine stream of bubbles which spread in all directions up the slope of the bulging gas cell. A few more slashes and the cross-shaped hole with its inch-long arms was gushing Dhrawnian air in a flood of bubbles that made the work invisible. The prisoners ceased their efforts. Slowly but visibly the stretched fabric was collapsing. The bubbles fled more slowly across its surface, gathering at the high point near the wall of ice. For a few moments Beetchermarlf thought the fabric would go entirely flat, but the weight of the suspended truck prevented that. The center of the cell or the point at which the truck was attached (neither of them knew just where the cell boundaries were) was straining downward: it was now pull instead of push. “I’ll start the engine again and see what happens,” said Beetchermarlf. “Get forward again for a minute.” Takoorch obeyed. The younger helmsman deliberately wedged a number of pebbles under the front ends of the treads, climbed the truck once more and settled down. He had kept the light with him this time, not to help him with handling controls but to make it easier to tell how and whether the unit moved. He looked at the point of attachment a few inches above him as he started the engine once more. The pebbles had provided some traction; the fabric wrinkled and the swivel tilted slightly as the truck strained forward. An upper socket, inaccessible inside the cell, into which the shaft telescoped, prevented the tilt from exceeding a few degrees. The trucks, of course, could not be allowed to touch each other but the strain could be seen. As the motion reached its limit the trucks continued moving, but this time they did not race free. Sound and tactile vibrations both indicated that they were slipping on the pebbles and after a few seconds the feel of swirling, eddying water became perceptible against Beetchermarlfs s air suit. He started to climb down from the truck and was nearly swept under one of the treads as he shifted grips. He barely stopped the motor in time with a hasty snatch at the control. He needed several seconds to regain his composure after that; even his resilient physique could hardly have survived being worked through the space between treads and rocks. At the very least, his air suit would have been ruined. Then he took time to trace very carefully the control cords leading from the reactor to the upper guides along the bottom of the mattress, following them by eye to the point above the next truck forward where he could reach them. A few seconds later he was on top of the other truck, starting the motor up again from a safe distance and mentally kicking himself for not having done it that way from the beginning. Takoorch reappeared beside him and remarked, “Well, we’ll soon know whether stirring water up does any warming.”

“It will,” replied Beetchermarlf. “Besides, the treads are rubbing against the stones on the bottom instead of kicking them out of the way this time. Whether or not you believe that stirring makes heat, you certainly know that friction does. Watch the ice, or tell me if the neighborhood is getting too hot. I’m at the lowest power setting, but that’s still a lot of energy.” Takoorch rather pessimistically went over to a point where the cairn should be visible if it were ever freed of ice. He settled down to wait. The currents weren’t too bad here, though he could feel them tugging at his not-too-well-ballasted body. He anchored himself to a couple of medium-sized rocks and stopped worrying about being washed under the treads. He did not really see how merely stirring water could heat anything but Beetchermarlf. point about friction was comforting. Also, while he would not have admitted it in so many words, he tended to give more weight to the younger sailor’s opinion than to his own and he fully expected to see the ice yielding very shortly. He was not disappointed; within five minutes he thought that more of the stony bottom was becoming visible between him and the barrier. In ten he was sure, and a hoot of glee apprised Beetchermarlf of the fact. The latter took the risk of leaving the control lines untended to come to see for himself and agreed. The ice was retreating. Immediately he began to plan. “All right, Tak. Let’s get the other units going as fast as they melt free and we can get at their controls. We should be able to melt the Kuvmbly loose from this thing, besides getting ourselves out from under.” Takoorch asked a question. “Are you going to puncture the cells under all the powered units? That will let the air out of a third of the mattress.” Beetchermarlf was taken slightly aback. “I’d forgotten that. No, well, we could patch them all, but-no, that’s not so good. Let’s see. When we get another power unit clear we can mount it on the other truck that’s on this cell we’ve drained already; that will give us twice as much heat. After that I don’t know. We could see about digging under the others-no, that didn’t work so well-I don’t know. Well, we can set one more driver going, anyway. Maybe that will be enough.”

“We can hope,” said Takoorch dubiously. The youngster’s uncertainty had rather disappointed him, and he wasn’t too impressed with the toned-down substitute for a plan; but he had nothing better himself to offer. “What do I do first?” he asked. “I’d better go back and stand by those ropes, though I suppose everything’s safe enough,” replied Beetchermarlf indirectly. “Why don’t you keep checking around the edges of the ice, and get hold of another converter as soon as one is unfrozen? We can put it into that truck,” he indicated the other one attached to the deflated cell, “and start it up as soon as possible. All right?” Takoorch gestured agreement and started surveying the ice barrier. Beetchermarlf returned to the control lines, waiting passively. Takoorch made several circuits of the boundary, watching happily as the ice retreated in all directions. He was a little bothered by the discovery that the process was slowing down as the cleared space increased but even he was not too surprised. He made up his mind eventually which of the frozen-in power boxes would be the first to be released and settled down near it to wait. His attitude, like that of his companion waiting at the controls, cannot be described exactly to a human being. He was neither patient nor impatient in the human sense. He knew that waiting was unavoidable, and he was quite unaffected emotionally by the inconvenience. He was reasonably intelligent and even imaginative by both human and Mesklinite standards, but he felt no need of anything even remotely resembling daydreaming to occupy his mind during the delay. A half-conscious mental clock caused him to check the progress of the melting at reasonably frequent intervals; this is all a human being can grasp, much less describe, about what went on in his mind. He was certainly neither asleep nor preoccupied, because he reacted promptly to a sudden loud thud and a scattering of pebbles around him. The spot where he was lying was almost directly aft of the truck which was running, so he knew instantly what must have happened. So did Beetchermarlf, and the power unit was shut down by a tug on the control line before a man would have perceived any trouble. The two Mesklinites met a second or two later beside the truck which had been running. It was in a predictable condition, Beetchermarlf had to admit to himself. Mesklinite organics are very, very tough materials and the tread would have lasted for many more months under