by Hal Clement
IV
PERHAPS an hour later, after several more unanswered calls, they reached a spot where something seemed to have happened. There was a dark patch of irregular shape in the “snow.” The white deposit was now some half an inch deep on the plain; but here it seemed to have been cleared away. The edges of the bare region were sharp and well defined, though irregular. The men all reached the same conclusion at the same time; they had all shovelled too many snowy driveways to be fooled here.
“He scraped the stuff up to put in his tank!” exclaimed Frake. “That’s what he meant about water, all right—though he’ll spend a good long time getting up enough to make much impression on the ship’s tank, I should think. But hadn’t we better do the same? Our own fluid gauge is reading lower than I really like, at this distance from Moretus.”
“How about it, Al?” asked Imbriano. “Suppose this stuff is largely ammonia and/or methane? What would happen if we used it in the tractor?”
“Either one is all right so far as straight theory goes,” Detzel replied carefully. “They’re both low-boiling, low molecular weight compounds which would operate perfectly well in a turbine. I’m just afraid they might be a little too low boiling. That would cut down of efficiency, and at our working temperature their vapor pressures might be too much for our tank.”
“I was afraid of that. Is there any way we can make sure, safely?”
“I should think so. There are safety valves on the tanks—after all, even water is apt to get pretty hot if the tractor stands in the sun for long. The regular relief valves might keep things safe, but I could ease off their springs a bit to make them safer. If we don’t put too much of the stuff in at once, we might get away with it. After all, Ingersoll seems to have.”
“HE SEEMS to have loaded the stuff. We don’t know that he got away with it,” responded the doctor dryly. “I suggest, Al, that we quietly put one pinch of the stuff in the tank and see what happens—in fact, could we draw a bucket or can or something of water from the tank and put our pinch of snow in that, at some distance from the tractor? I admit I’d be happier that way.”
“I guess a cup of water would last long enough for that. We’ll try, anyway.” The three men donned their helmets, pumped a reasonable fraction of the cab’s air into the low-pressure economy tank, and opened up. Detzel found a paper drinking cup and stepped out, making his way around to the trailer which carried the, fluid tank. There he bent, held the cup under a stop-cock, and quickly opened and, closed the latter. Water squirted out violently; it was warm enough to have a vapor pressure of several centimeters of mercury. The stream of liquid hit the cup and splashed, but enough remained inside to be useful. Detzel grimaced behind his face plate.
“Offends my economical soul,” he remarked, staring at the bubbling, frothing liquid.
“You’ll be wasting more if you don’t get moving,” retorted Frake. “Get some of the snow in before everything boils away.”
Detzel obeyed. He took a small scraper from its place on the side of the trailer and walked over to the edge of the clear area. He set the cup on the ground where the men could see it; Frake was holding the beam of a flashlight on the scene. He picked up a bit of the snowy material on the end of the scraper, and tipped it into the cup.
The results were spectacular; as Imbriano said a moment later, “Water holds quite a bit of latent heat, doesn’t it?” The contents of the cup fountained skyward and failed to return, fading into invisible vapor before the moon’s feeble gravity could do much about it. The cup itself was intact, but the fact was rather surprising to the witnesses.
“I don’t think any valves made will take that, or let the tank take it,” Detzel remarked “I’m afraid we’ll have to depend on what’s still in the tank to get us back to the ship.”
“WHAT?” Even Imbriano was startled to hear the dry voice of Ingersoll in his headset once more. “What? Can’t the brilliant doctor solve such a simple problem? Even when he just mentioned the answer? But of course, you have a slight disadvantage. You have only one fuel tank, haven’t you? I very carelessly brought the spare with me. It was empty when I filled it—with snow, friends—no water. No stored heat to speak of. I’ve packed the snow into it, and we’ll just let it melt very slowly, and the methane can evaporate quietly through the valves, and the ammonia stay in solution if it wants . . .
“I’ll tell you what, good doctor: why don’t you just dump all your water out of that tank? Then in a little while it will be cool enough to take the snow safely, and you can go back to starve with your friends—for you can’t catch me, can you? I have two tanks, and that makes the big difference, doesn’t it? I’m going, by the way, and—I’m sure you can see me with your instruments, but you can’t follow. You don’t dare go any way but back to Moretus, do you? Of course, I’m not going far either—I’m not going to take this tank out into sunlight for a while—but you don’t dare even chase me around in circles, do you? Fuel is getting a little short.”
He broke off as abruptly as he had started. The drivers looked at the doctor. He shrugged invisibly in his suit, and led the way back inside the cab. There, with air once more about them and their helmets off, Frake finally spoke up.
“Well? Was he right?” He was looking at Imbriano as he spoke.
“I’m not the engineer,” the doctor said wearily. “So far as I can see, he is perfectly right. Personally, I’m optimistic about the fuel in the ship’s tanks. I don’t think we could possibly have lost much before the ice layer formed. But that doesn’t make me any happier about Ingersoll.”
“Maybe we’d better tell him about the ice stopping the evaporation,” suggested Frake.
“You do it. He certainly wouldn’t believe me,” the doctor replied wearily. Frake took the microphone.
HE CALLED Ingersoll’s name several times, without answer; then he told about the freezing in the tank, sure that the other was listening. He ended with an air of frankness.
“I admit we don’t know there’s enough to get us home,” he said, “but you know I’m talking sense when I say there’s a good chance of it. If you want to take that chance, just stay where you are and watch. You can probably see the takeoff from here. You’ know about when it will be—you can guess how long it will take us to get back. We’re starting now. You can stay or come, as you please.”
He hung up the microphone and Detzel started the tractor out toward the sunlight, slanting back toward the foot of the trail leading down from the rim. Imbriano rode with head turned over his shoulder, in the general direction that he believed the other vehicle to be. There was sound from the radio.
But it was Detzel who saw the other machine, and called their attention to it. It was parallelling their course, half a mile to the north, and gradually pulling ahead of them. It was just barely visible; almost all that could be seen was scattered light from its lenses, and the streak of illumination stretching over the ground ahead of it. Detzel took the microphone.
“Glad you’re coming, Milt,” he called. “Want to lead? You must know this road enough better than we do, so you can go faster safely.” There was a brief pause.
“All right. Pull over this way, and fall in behind me.” The voice had lost all trace of emotion. Detzel slanted obediently to the left, and relaxed a trifle—he had been giving close thought to the problem of navigation. Imbriano did not; and it was just as well.
THEY WERE a scant hundred yards from the other machine, and were just about able to make it out in the light now reflected from the mountains, when Detzel’s attention was jerked back to full operational level. With a turn that threatened to snap the couplings of its trailers, Ingersoll’s tractor was whipping around; its lights glared directly into their eyes, and Imbriano and Frake ducked instinctively. Fortunately, Detzel’s reactions were of a more constructive nature; he wrenched their own vehicle to the right, and managed to avoid the first charge.
“Get your helmets on!” he snapped to the others. “Then take the wheel, Bil
l, while I do mine. If he even grazes us there’ll be no air in this cab!”
“We can outrun him. He’s pulling a bigger load,” the doctor pointed out as he fitted his helmet in place.
“We could on the straight—but we’re not sure we can go straight. If anyone knows the crevasses around here, it’s Ingersoll, not me.”
“Even he shouldn’t know them too well. He can’t have spent all his time exploring cracks,” Frake put in optimistically.
“He doesn’t have to know them at all to have a big advantage,” snapped Detzel. “The sad fact is that we’re going first. If we can keep going, he can. We can keep ahead just as long as I don’t have to detour.”
“Head out into the sunlight!” cried Imbriano. “He won’t dare take that trailer of snow out there. It would boil too fast.”
“We don’t know what he’d dare. It’s a metal tank, and would take a while to heat up. And if he’s willing to risk his own life in a collision, he can’t be very rational anyway. I’m already on the way toward sunlight, in case you hadn’t noticed.”
“Put on more juice! He’s catching up!” called Frake. Detzel tried, but the turbine was already whirling at its safe limit.
“Something’s wrong. Our trailer must be dragging,” he snapped. “We didn’t take time to service it properly before we set out on this junket.”
“That’s not it. I can see now. The back right tire is flat. Either it picked a gruesome time to hit something sharp, or Milt nicked it on that first pass.”
“IF WE CAN’T outrun him, we’ll have to outmaneuver him,” grunted Detzel. “We should still be able to make tighter turns than he can, tire or no tire. Tell me when he’s about twenty yards back.”
“He’s closer than that already, I’d say, though it’s hard to be sure with the lights right in my eyes.” Detzel’s answer was another twist to the right. At the same moment Imbriano started the economy pump since they all had their helmets sealed by this time. Neither of the others noticed. Detzel would probably have objected to the waste of power if he had.
The turn was almost, but not quite, successful. The other machine grazed the rear of the trailer, some projection on it ripping their other back tire. Fortunately, the fuel tank front made the trailer’s center of gravity a trifle ahead of middle pair of wheels, so it didn’t settle too badly on back ones except under acceleration; but the additional flatting of the middle tires added quite a bit of drag.
For a moment, it looked as though Detzel might be overcoming this disadvantage. He held his turn, and the other train was unable to match it, as he had hoped. Slowly he drew ahead; then he was parallel, going the other way; then drawing up behind as he lapped Ingersoll. Then they were traveling only a yard or two away from the back trailer of the other machine, and matching its angular speed. As they reached this point, Imbriano opened the door by his seat and swung out.
For a moment, neither of the others noticed. By the time they did, he was climbing across the back of the cab and almost within reach of Ingersoll’s rear trailer. He reached, but couldn’t quite make it.
“Closer, Al,” he snapped. The others heard his voice, didn’t for a moment realize where he was since the suit radios gave little indication of distance, and Detzel obeyed the without asking why. Then Frake looked back, discovered the doctor missing, and after, added a moment located him.
“Doc! You idiot!” he cried. The call distracted Detzel, but fortunately not enough to disturb his driving. “What’s the matter?” he asked without taking his eyes from the other.
“Doc’s climbing onto Milt’s trailer! He’s nuts!”
“SHUT UP, stupid!” Imbriano’s voice came. “Well, never mind. It’s too late now.” Frake had forgotten that they were now using the suit radios, and Ingersoll could hear anything they said. The doctor, with secrecy at an end, addressed the geologist directly.
“Here I am, Milt. Right on your rear trailer. Any ideas about how to run into me now? You might as well leave the other tractor alone. Getting it won’t get me, will it?”
The answer that came back was unprintable, except for the concluding sentence: “Anyone who helps you needs squashing, too.” The larger train swerved away and slowed down, trying to bring Detzel ahead, but the engineer was alert and held his position to the other’s right rear.
Imbriano, holding firmly to the body of the trailer, spoke again. “Don’t waste too much fuel, Milt. You may find you don’t have much to spare, after all.” He began to crawl forward along the train as he finished speaking. The bodies of the vehicle were mostly empty—they never knew why Ingersoll had taken so many—and the spare tank containing the snow was bolted to the front of the second one in line. The tank on the first was, of course, actually in service.
Reaching dangerously around the snow tank, Imbriano found the pin of the coupling which connected the trailer to the one in front, and pulled.
He was unable to move it; there was too much tension on the coupling as long as the tractor was pulling. There were several cases on the front trailer, however—probably the missing food—which prevented Ingersoll from seeing what the doctor was doing; and this uncertainty led the geologist to solve the other’s problem for him.
Thinking that Imbriano was damaging his precious reserve tank, Ingersoll began randomly braking and accelerating in an effort to shake him off. This was nearly successful, but it also enabled the doctor to work the pin free after a few cycles, since each time the push changed to a pull or vice versa there was an instant when it was loose. At last he got it out, and had the satisfaction of seeing the tractor and front trailer bound away from him as Igersoll applied power once more.
THE GEOLOGIST realized instantly what had happened, cut around in as tight circle as he could to bring his lights on the trailers and Imbriano, and stopped. He evidently wasn’t ready to come out; it was too dark to see inside his cab—especially past lights—but the pause suggested that he was helmeting up and pumping back his air. Imbriano assumed that he was preparing to come out anyway, and thought of a delaying move.
“Just a minute, Milt—don’t come out yet. If I see your door open, you’ll see this stop-cock do the same thing. How about it?” Imbriano had his gloved hand on the bottom tank drain.
For a moment there was silence. Then, “Go ahead and open it. Here I come!”
The doctor couldn’t see the cab door open beyond the lights, but he wasn’t looking anyway. He carefully opened the stopcock and sprang back, expecting a jet of vapor comparable to the one from the cup not long before: He was watching for it so anxiously that he almost didn’t see Ingersoll coming, for the watching job took no longer than he had expected. Nothing happened.
Fortunately for the doctor, Ingersoll had seen the whole thing, and he came to a stop beside the trailer and laughed. “Smart boy, Doc. I suppose you expected the stuff to boil right out and leave me stranded didn’t you? You didn’t remember that the tank has never been in the sun since it was filled; and it had no water in it, and had been out of the sunlight long enough to cool down even before it was filled. Where did you expect the energy to come from? Or doesn’t the medical profession believe in conservation of energy? Why, you little . . .” his language became profane and irrelevant once more, and he made a leap in Imbriano’s direction.
The doctor had plenty of time to get out of the way; and his own leap took him out of the direct beams of the headlights, so that for a moment he effectively vanished. Ingersoll started to follow; then a flash of reason crossed his mind, and he headed back for the cab of his own tractor. He got the idea more quickly than any of the others, and made it with plenty of time. He had left the turbine idling, so there was no delay in starting, and neither the doctor nor Frake, who had also leaped from their tractor the moment Detzel brought it to a halt, had a chance to get aboard Ingersoll’s.
“Get back with Al!” called Imbriano. “Get back in the tractor, and keep it out of the way. I’m safe enough. Maybe he’ll cool down enough to reason with after
he’s made a few passes at me. Unless he’s taught that machine to jump, he’ll never catch a man on foot with it!”
Frake agreed, though his words were nearly drowned in another flood of language from Ingersoll. Imbriano was promptly given the opportunity of proving his claim that he could keep out of the way of a tractor.
HIS IMGINATION supplied the thunderous turbine whine which the lunar vacuum could not transmit. Some sound, but not much, came through tracks, ground, and feet; but practically, the chase might have been recorded on an old silent film. Frake, later, claimed he was surprised not to see subtitles; but his sense of humor was not very subtle.
Imbriano was not feeling humorous at all. He was able to dodge, all, right, but it was not very easy, and he was afraid of leaping too far. A bad landing could be disastrous, since not very much has to go wrong with a space suit to kill its occupant. After a few passes which would have won very little applause in a Spanish bull-ring but were quite as exciting for Imbriano as he wished, it occurred to him that Ingersoll might be a little slower if the dodging were being done around his precious reserve tank. Accordingly, the doctor made his, next leap or two in this direction, and began playing tag around the stranded trailers.
He was still hoping that Ingersoll might cool down and be reasonable; but there was no sign of such an event, and he couldn’t think of anything to say that might have a calming effect. Throughout the affair, he had been worried by the feeling of guilt he had expressed earlier, and the we may have slowed him down—certainly some of his escapes were narrower than they needed to be.
Then a different feeling began to take hold of him. However reasonable Ingersoll’s initial resentment may have been, this grimly-determined effort to repay unpleasantness and discourtesy with murder was going a little too far. Imbriano’s sympathy and guilt-feeling began to give way to resentment and anger; his temper, never outstandingly good, was wearing thin. He was thinking, now, in terms of force rather than persuasion. But that did him little good; granted that a man on foot could keep from being harmed by the man in a tractor, there seemed nothing whatever he could do on the offensive. Certainly Imbriano could think of nothing. He kept as close as he could to the stranded trailer, answered the questions of Detzel and Frake as reassuringly as his breath permitted, and kept moving. He didn’t get onto the trailer itself; later he convinced himself without much trouble, that his own subconscious kept him off.