"The hypers.p.a.ce units-the power for them-" Wilfred began.

"If we ever find a way to power them, it will have to be en route in s.p.a.ce," Taylor said. "Or that's the safest course of action for us, I would say."

"I agree," Blake said. "If we can find ore pure enough, we might possibly be able to take off from here within six months. It would have to be exceptionally pure ore-it's improbable that we can find such ore but we don't know that it's impossible. The first thing we want to do is to start getting as far away from here as possible, and as fast as possible. Given pure enough ores, we can do that, I think."

"You said 'improbable but not impossible,' " Taylor said. "Just how improbable do you think it is?"

"If the other ranges are similar to this one, our chances are very poor. We can try; we can go out as two different parties to save time. Cooke has had experience in the hills, now, and could go with one of you to the range north of us while I went with the other to the range south of us. If there's nothing in the adjoining ranges, I would say there is no use looking farther."

"Why?" Lenson asked.

"Time. Time and distance. Any ore we found would have to be carried to the ship on our backs-the truck is worn out."

"Then let's start today," Cooke suggested. "Since our time is so short, we shouldn't waste an hour of it. Let's start right now."

Blake glanced at the early morning sun. "A good idea. We certainly won't have any days to waste. We'll take along about sixty days' supply of concentrated food tablets, plus spare shoe soles and, above all, canteens."

"The concentrated food tablets for two months-" Wilfred began doubtfully, but was interrupted.

"For roughage we can eat thorn berries," Blake told him. "Cooke and I tried them.

They're tasteless, but they're completely harmless." He turned to Cooke. "You can take Wilfred across to the north range, and Lenson is better built for the hike across the desert to the south range than Wilfred is-it will be about three days on the water in our canteens to reach that south range."

"And if the south range has no creeks or springs in it-how will you come back across the desert without water?" Taylor asked.

"We won't," Blake said simply.

Cooke slid off the fender and looked at the truck, shaking his head. "If only we could have had this truck to use-"

Blake and Lenson reached the south range on the third day of tramping across the glittering diamond sand of the desert, their throats burned and dry and their canteens empty. They found water; a seepage of sickening alkali water, but it was water. They found a creek of sweet water the next day as they started up the range's northern front, tumbling down out of the mountains and disappearing beneath the sand at the mountain's foot. It was a high, rugged range and they found other creeks and springs as they went.

They reached its eastern end on the thirtieth day and turned down its southern face. They came to the last canyon on its southwest slope on the fiftieth day and knew they had failed. They had found an occasional vein of iron oxide and, once, a fairly soft vein of copper ore, but there had been no indications of uranium.

On the fifty-fourth day they reached the ship again, gaunt and ragged, with Blake's red whiskers flaming riotously and Lenson's brown beard giving him the look of a benign but dest.i.tute young religious father. As though by prearranged plan, Cooke and Wilfred returned at the same time; Wilfred's pink face burned red by the sun, his blond whiskers sprouting raggedly, while Cooke wore a bushy black beard that, together with his glittering black eyes, gave him an even greater appearance of piratical fierceness.

Taylor was carrying two buckets of water to the ship when the four of them appeared.

He set the buckets down and waited.

"No luck," Blake said as they drew near him.

"Same here," Cooke said. "That range we went to was as barren as this one."

"I've been continuing my observations," Taylor said. "Everything checks with my first ones, and now we're sixty days nearer the end. We'll have to start accomplishing something pretty quick."

"I know it," Cooke said, scratching at his black beard, the tattered sleeve of his shirt flapping in the wind. "But before we start any long talks on what we shall do next, let's have something to eat besides thorn berries and pills. And take a bath-I'm so covered with diamond dust that, in the nude, I'd glitter like a precious jewel."

Taylor picked up his buckets of water. "There's enough water for all of you to take showers," he said, "so long as you don't waste it. I've been busy with other things or I would have had more water carried to the ship."

"We'll have to have a pump," Blake said, relieving Taylor of one of the buckets.

"There's no use spending time carrying water in buckets."

Lenson looked at him sharply to see if he were joking.

"Did you take a look at what that diamond silt in the water did to our pump?" he asked. "It ruined it, and it was made of the hardest alloy steel."

"We can't use any kind of pump that has moving parts of steel," Blake said. "No steel alloy ever made can resist diamond. And, since steel is our hardest man-made material, it's obvious we can't use any kind of a pump that has metal moving parts. So, we'll not try to fight the diamond with harder steel alloys-if we had them-we'll just overcome the abrasion problem by making a pump that has no moving parts."

"Oh?" Cooke stared at him. "A brilliant solution but for one thing-how do we move water without the mover doing any moving?"

"We let the water use its own velocity to force part of itself higher than the source- we make a hydraulic ram."

"Hm-m-m!" Taylor grunted in self-disgust. "I could have had one made long ago, in my spare time, but I never thought of such a simple solution. I kept thinking of some way to combat the diamond's abrasion, rather than how to avoid it completely."

"But a hydraulic ram does have moving parts," Wilfred objected. "The valves.

Without the valves alternately opening and closing, the ram wouldn't work. How do you keep valves in it?"

"The valves are so simple-one floating valve and one flap valve-that all we have to do is spray the valves and valve seats with plastic rubber. The diamond can't harm rubber-the rubber is so soft that the diamond's hardness has no effect on it."

A shower and a full meal did much to improve their spirits, and a shave did even more to improve their appearance. Taylor brought up the subject of their next course of action and asked Blake for his opinion of the desirability of further prospecting for uranium. Blake answered the question with a suggestion.

"We'll have to rest a week, even though our time is so short," he said. "This time we'll have two deserts to cross, as well as the mountain between, and our past sixty-day diet of food tablets and thorn berries has all four of us in pretty weak condition. While we rest up I suggest we try to think of some alternative to the atomic drive. I won't argue if the rest of you want to continue looking for uranium, but I'm afraid it's hopeless. Without a truck or any other form of transportation, it would do no us good to find the ore. We're not going to be given the time to carry ore for great distances on our backs, across deserts and mountains. So, suppose for the next six days everyone makes a try at thinking up some plan other than the atomic drive?"

"The more plans, the better," Taylor said. "If we had a large enough selection to choose from, we could pick out one that would be sure-fire. But I can't see how we can find a quicker and simpler way to lift this ship than the atomic drive."

The others felt the same way; they seemed quite willing to consider any alternate plan but with no conception of any such plans. Blake made no mention of the idea in his own mind, certain that it held their only hope for survival but fearing its radical departure from conventional lines of thinking would cause them to reject it, despite the magnitude of its possibilities.

They made the hydraulic ram the next day and laid a line of the ship's air tubing to a point sufficiently upstream along the noisy little creek to give the necessary pressure.

Shortly before the sun went down they connected the last length of tubing to the ram, then returned to the ship to wait for the first flow of water into the ship's tank. It required some time for the tubing between the ram and the ship to fill with water but the water came at last; a steady little trickle.

"You know," Cooke remarked as he watched the tiny flow, "those ancients weren't exactly fools."

"At last, we've won one round in our battle with this diamond dust," Lenson said.

"I want all of you to keep in mind how we did it," Blake said. "We did it by using the natural forces at hand and by not trying to fight the abrasiveness of the diamond grit.

Remember this, in any planning you do-you can't fight diamond with metal!"

"I think we're all aware of that by now," Taylor said.

"I hope so. Until we acknowledge that fact, we won't get anywhere."

No further mention was made of their problem in the succeeding days and Blake hoped that such silence was indicative of serious thinking on their part and not merely a fatalistic acceptance of the status quo.

On the sixth day following their return they gathered in the central room of the ship for each to present his plan, if any. Blake procured a few small items from the repair room and his own locker just before the discussion began.

Taylor made a quick summary of their predicament.

"There could have been only three possible ways of leaving this planet," he said. "The most certain would have been to send a message to New Earth, but that's impossible. We can't repair or duplicate the smashed transmitter tubes or hypers.p.a.ce transformer. Their construction calls for very complex precision machinery as well as special alloys. We can't re-use the various alloys in the shattered tubes because exposure to the air has turned several of the more delicate alloys to dust.

"The second easiest method, and the most impossible, would be to simply wait and hope a ship comes along in time to save us. I know that we all reject that. That leaves only one way of leaving this world before it burns-to make a drive for our ship. And that boils down to the question: Shall we continue to search for uranium and cadmium or shall we devote our time and effort to some other method of lifting the ship than an atomic drive?"

"I've kept my mind a receptive blank for six days and not one single idea has come near it," Lenson said. "I don't see where we have any choice-what else can we plan on with any hope at all other than an atomic drive?"

"Before we go on to new plans," Wilfred said, "suppose we let Blake give his opinion of the chances of finding uranium and cadmium in time to make a drive."

"We haven't found any evidence of any uranium in three full-grown mountain ranges," Blake said. "There's iron, and a small amount of copper, but no radioactive elements. I don't know whether it's true of all this continent, but the section we're on is almost wholly light elements.

"I am not in favor of any further prospecting. Our time is very limited; anything we do will have to be done without delay. Further prospecting, on foot, would require time, lots of time. Possibly the ore we want is within fifty miles of us, but how do we find it in time, on foot? Even if we found it, and in a sufficiently pure state, how do we transport it back to the ship in time? We have no truck, you know; we have only our legs and backs.

If we had the time-and if this world permitted us to use the truck-I would be in favor of continuing the prospecting until we did find the ores we needed. The truck would shorten days of travel into hours; it would haul needed supplies and equipment to the ore and haul the ore back. But we don't have a truck any more-and we don't have the time.

In my own opinion, further prospecting is a waste of our short and precious time."

"There doesn't seem to be anyone who disagrees with you," Taylor said when the others remained silent. "You paint a dark picture, but there's no denying the truth of it."

"Do you have a plan?" Wilfred asked.

"I have. You've all been thinking along conventional lines, haven't you?"

"Such conventional lines of thinking produced the ship that brought us here," Wilfred pointed out.

"It did, but the same conventional type of thinking is never going to lift it up again. I have an unconventional idea, and a deceptively simple question. If you can answer my question, we'll know how to make a drive for our ship."

Blake extracted several items from his pocket: a short steel bar, a square of sheet aluminum, a piece of thin gla.s.s and a large darning needle on a long thread. He laid them down on the table before him and continued: "I'm afraid that conventional thinking won't work on an unconventional world. We've all been tackling our problem as though we were marooned on a counterpart of New Earth, with New Earth's dust-free air and plentiful supply of minerals. We keep thinking of a rocket drive because a rocket drive was the simplest type of drive to build on a world of machinery and radioactive ores. We have neither, here; we don't have Earth-type resources and equipment to fight a decidedly non-Earth-type environment. On New Earth we would use machines-all human technological progress stemmed from that simple little thing, the wheel. Without wheels there would never have been machinery, without machinery there would never have been the atomic drive. You've all seen that we can't have wheels on this world. We can't have wheels, we can't have any kind of moving-parts machines on a world of diamond dust. Our own science is built on the wheel and if we don't develop a subst.i.tute science for it, we go up in smoke in seven or eight months."

Blake picked up the steel bar. "There is one force that no one has mentioned, and it's a force that all the diamond dust on this world could never faze because it has no moving parts-field-type force."

He picked up the needle by its thread. "This is a common bar magnet," he said, letting the needle click against the end of it. "We all know that opposite poles attract, like poles repel. I pull the needle off the end of the magnet and the needle snaps back against it the moment I release it because its lower end has been magnetized with a polarity opposite to that of that end of the bar. If I switch ends with the bar magnet, the needle, instead of being attracted to it, will swing away out on the thread to stay away from it. I have a piece of sheet aluminum here-the magnetic repulsion goes right through it. The same with this piece of gla.s.s."

He laid the magnet and needle back down on the table. "You four have the technical training and knowledge-I'm only a fairly competent mining engineer. But my common sense tells me the reason we can't leave here is because a field-type force, gravity, holds us here. My common sense also tells me that there must be the same basic principles underlying all field-type forces; magnetism, induction, gravity. If two magnetized bodies can be made to repel each other, is it impossible that two bodies held together by gravitational attraction could be made to repel each other?

"As I said, I think the same basic principles underlie all field-type forces. If we can learn what that principle is, we can produce a drive that operates by antigravity. So, this is the question I wanted to ask you: What caused the needle and magnet to behave as they did?"

There was silence for a while as they considered Blake's proposal. Wilfred was the first to speak.

"It's a simple phenomenon," he said, "and known to any child."

"That's true," Blake agreed. "Any child knows what a magnet will do, but do any of you know any more about a magnet than the hypothetical child? You all know what a magnet will do-do any of you know why it does it?"

"I know nothing of magnetic forces, myself," Lenson said, somewhat uncertainly, "since they don't enter my own field of study, but Cooke probably knows them from A to Izzard."

"I know what a magnet will do-I don't really know why it does it," Cooke said.

"Men have made use of magnetism and induction forces for centuries and the behavior of such forces is known in precise detail-but still no one knows just what these forces are.

You can manipulate a force to your own advantage if you understand its behavior under various conditions, but if you understand exactly what that force is, you can manipulate it to your own advantage much more efficiently." "I agree," Lenson said.

"There's another field-type force we use without fully understanding it-our hypers.p.a.ce drive," Blake said. "Theoretically, it shouldn't require such an enormous surge of power to activate the s.p.a.ce-shift units-but we have to use that enormous surge of power to get any results. We say we 'slip' or 'jump' into hypers.p.a.ce. We don't. We don't 'slip' through that barrier-we smash our way through it with the full output of a nuclear converter. If we can learn what field-type forces are, I see no reason why we might not be able to so alter our hyperdrive that the ship's generator will supply more than enough power for it."

"A possibility," Cooke said.

Taylor nodded in agreement, then said, "But, while the idea has unlimited possibilities, we haven't the slightest a.s.surance that we'll realize any of them in the short time we have."

"I know it," Blake said. "I know it's a long chance, since our time is so short. But it is a chance, and all the other plans would have been doomed to failure before we started."

"It's something of a challenge," Wilfred said. "The idea appeals to me. It's true that we actually know relatively little of field-type forces; our environment was such that our technical progress led to atomic study."

Blake looked the four men over, both surprised and relieved that they should accept his plan without argument; the only possible approach to the problem, he was convinced, that offered any hope. Taylor seemed to be the only one who had any doubts and Blake said to him, "What is your own opinion of my plan? Are you in favor of dropping all other plans and concentrating on the study of field-type forces?"

"My half-expressed doubts about accomplishing anything in the time we have weren't intended as an objection. It's a field of study of which we know very little, and it's a difficult field to learn. But I'm in favor of it-it, at least, isn't dependent upon the use of moving machinery. We can study it under controlled conditions, here in the ship. In fact, I would like to suggest the study of induction fields as a starter-we can manipulate induction fields to suit ourselves, and under all kinds of conditions."

"In all of Man's history," Cooke said, "since the first savage wondered why a piece of natural lodestone would attract grains of magnet.i.te, no one has been able to discover why. But, while we don't have much time, we have a very powerful incentive. And we do know a few things about magnetism. For example: all ferrous iron with a valence of two is magnetic. Ferric iron, with a valence of three, is not magnetic. Let's find out why-an atom of iron is an atom of iron and should be magnetic whether it's combined with oxygen or not."

"We'll need juice," Taylor said. "Plain, old-fashioned electricity."

"We can manage that," Blake said. "The ship's generator wasn't damaged, so we'll make the only kind of engine a world without oil, coal or radioactive ores would have permitted-a steam engine. We have water, plenty of trees for fuel, and we have a lathe.

There's a spare primer-thrust tube that will make a perfect cylinder."

"How about the diamond dust in the water?" Taylor asked.

"Only clean steam will go to the cylinder, and the diamond dust won't affect the boiler as lime would. Besides, we have our water filters on the ship's tanks."

Wilfred picked up the needle and let it swing from the thread, holding the magnet under it. "If this magnet represented this planet, and its magnetism was the force of gravity, with this needle representing our ship, fitted with some gadget to make it antigravitic at the lower end as this needle is antimagnetic-"

He let the needle swing on the thread, bouncing away from the repulsion of the magnet, then swinging in again, to be stopped and driven away by the invisible force.

"The invisible barrier," he said. "What is it? It isn't matter-not as we know matter.

We call it a force, but just exactly what is it that no material-gla.s.s, metal or anything else-can bar?"

"That's the question," Taylor said. "It's going to be a hard one to answer."

"It will," Cooke said, "but we know the answer is there if we can find it. The power we need to move this ship is all around us; we'll be looking for the secret of a power that we know exists."

"And if we continued to hunt for uranium, we'd be looking for something that all the evidence shows does not exist," Blake said.

Lenson shoved back his chair and got to his feet. "Now that we know what we want to do, let's get busy," he said. "It will take all five of us quite a while to build that boiler and engine, so let's get started right now."