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 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, and settled himself 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 up could heat anything, but Beetchermarlf’s 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 his own, and he fully expected to see the ice yielding very shortly.

He was not disappointed; within five minutes he suspected that more of the stony bottom was 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 Kwembly 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. 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 the round of 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 but 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, and 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 many more months under ordinary travel wear; but deliberately rubbing against unyielding rocks under even very modest engine power was a little too much for it.

Perhaps the word “unyielding” does not quite describe the rocks; those which had been under the moving bad of fabric were visibly flattened on top by the wear of the last hour or so. Some of them, indeed, were more than half gone, and the young helmsman decided, after a careful examination, that the failure of the tread had been due less to simple wear than to a cut started by a formerly spherical pebble which had worn down to a thin slice with sharp edges. Takoorch agreed, when the evidence was pointed out to him.

There was no question about what to do, and they did it at once. In less than five minutes the power converter had been removed form the damaged truck and installed in the one aft of it, which had also been unloaded by puncturing the pressure cell; and without worrying about the certainty of destroying another set of treads, Beetchermarlf started this one up promptly.

Takoorch was uneasy now. The reasonable optimism of an hour before had had the foundation cut from under it; he was doubtful that the second set of treads would last long enough to melt a path all the way to freedom. It occurred to him, after some minutes wrestling with the question, that concentrating the warmed water on one spot might be a good idea, and he suggested this to his companion. Beetchermarlf was annoyed with himself for not having thought of the same thing earlier, and for half an hour the two labored heaping pebbles between and around the trucks surrounding their heat source. They eventually produced a fairly solid wall confining some of the water they were heating to a region between the truck and the nearest part of the ice wall. Takoorch had the satisfaction of seeing the ice along a two-yard front toward the starboard side of the Kwembly melting back almost visibly.

He was not completely happy of course. It did not seem possible to him, any more than it did to Beetchermarlf, that the treads could last very long on the second truck either; and if they went before the way out was clear, it was hard to see what else they could do toward their own salvation. A man in such a situation can sometimes sit back and hope his friends will rescue him in time — he can, in fact, carry that hope to the last moment of consciousness. Few Mesklinites are so constituted, and neither of the helmsmen was among the number. There was a Stennish word which Easy had translated as “hope,” but this was one of her less successful inference from context.

Takoorch, driven by this undefinable attitude, stationed himself between the humming truck and the melting ice, hugging the bottom to keep from deflecting the warmed current of water, and tried to watch both simultaneously. Beetchermarlf remained at the control lines.

Since no digging had been done under the second truck, the friction was greater and the heating effect stronger — the control was for speed rather than power, in spite of the words the helmsman had used. Naturally but unfortunately, the wear on the treads was also greater, and the heavy thud which announced their failure came annoyingly soon after the complete of the rubble wall. As before, the two bands of fabric gave way almost simultaneously — probably the jerk imparted to the drive shaft as one let go was enough to take care of the other.