by Hal Clement
"That was a good thought, Pete," Bowen said as soon as contact had been established. "We are trying to figure out your little problem right now. It would be simple enough, except for the fact that we don't know how fast he would be able to travel; the slower he goes, the sharper the curve of his path will be, since Polaris will move farther for each mile he travels."
"I can see that. Maybe Dart and I could go twice as fast as our ordinary walk on the smoother ground while we were searching back there, but of course there's no way to tell whether all the ground Tumble will be crossing is as easy to cover. Besides, sooner or later he might realize that Polaris is fooling him."
"True, but if we assume that, we're licked before we start. All we can do is suppose that he keeps heading for that star, and guess at how fast he can go."
"You say that the problem itself is easy? How long do you think it will take them to get an answer?"
"Just a few more minutes. We can have his probable path on a map long before you can get here."
"Then I'm going to stay out, if you don't mind. You can tell me the course, and I'll plot it on my map; then I can get down again and start searching."
"Do you have a map? I thought yours had been ruined when you took them outside."
"Darn it, that's right. Hmmm. I guess I'll have to come back to the station after all. I'll go right out again, though, if you'll let me, Uncle Jim; I don't think we should waste any more time than we can help."
"We'll see when you get here. It will depend on how badly you need rest and food—or rather, how badly I think you need them."
"Well—all right. I'm coming. Is the radio beacon on?—never mind, I see it is. I'm on my way."
With the acceleration Peter was using, it did not take him long to reach the station, but he was some time getting aboard. He could not solve in his head the mathematical problem of meeting the moving station with a moving ship so that both had the same velocity when they met; he passed close several times, but was either a trifle off speed or a trifle off position. The "trifles" in each case amounted to several hundred miles an hour or several dozen miles of distance, and even Peter's usual calmness was wearing thin by the time he had his rocket hanging apparently motionless a few hundred feet away from the station. Getting in step with its rate of spin and setting the little ship into its dock presented no difficulty, since he had had to solve those problems after nearly every flight he had ever made, so a few more minutes found him eating a hasty meal while Bowen produced the map the mathematicians had marked.
It showed the range which terminated in the Mountains of Light, and a surprising number of the smaller hills in the area. It was easy enough to see where the rockets had landed; from here, several lines had been drawn representing Tumble's possible routes, assuming different speeds. They all started in the direction Peter and Dart had given and curved more or less abruptly to the right. The sharpest curves represented the slowest travel, since the moving "North Star" would turn him about half a degree an hour regardless of how fast he walked. Each line had an "x" on it to show the position corresponding to fifteen hours' travel, but the lines had been carried farther to allow for search time.
Several of the "fast-travel" lines reached a range of mountains about ninety miles from the landing point, which extended almost directly across them and pointed roughly toward the pole; several of the more curved ones reached the walled plain next to Shackleton which actually contained the pole. It was possible that some of the hills bordering this plain might be mistaken for the Mountains of Light by Tumble, according to a note on this part of the map. Peter looked at this for a long time.
"That's a lot of square miles," he said at last.
"I know," replied Bowen gloomily. "It's a lot better than the whole surface of the moon, though. Where do you plan to start? While you search, of course, he'll be getting farther along; and you can't go back for about twenty hours." Peter stared at him, but saw that argument would not help.
"Don't I know it. Of course, the farther along I start, the wider the area he may be in. I'm going down
as close as I can to the place we lost his trail........"
"But that will be dark then!"
"I know. That's why I said 'as close as I could.' I'll check for level areas where there should be dust that he'd have to walk on, and if and when I find any which seem to go across all the lines on this map, I'll land and look for his trail again."
"That seems sensible."
"What are Dart and Bart going to do?"
"I don't know. They're not back yet, and I haven't had a chance to talk to them."
"Do I have to wait for them when I go?"
Bowen looked long and thoughtfully at Peter. He trusted the young fellow's ability, and realized how he felt about Tumble—the friendship growing between the two had been obvious enough to everyone. Still, there was a great deal that no one knew about the moon, and certainly there must be dangers which no one had foreseen or could foresee; times might come when even the most careful and thoughtful person would need help. On the other hand, there was the danger to Tumble, a danger growing greater with each hour that passed—he could not possibly have any food, and could not have eaten it if he had. All these thoughts crossed Bowen's mind, and Peter could read them as though they had been spoken aloud. He would not have blamed the man for refusing permission for him to go alone, but to his relief Bowen finally said:
"Go ahead—a little early, if you want. If the station is above the horizon at that place within an hour or so of the time you get there it will be all right. When the boys finish sleeping I'll decide whether it would be better for them to join you or search other areas, but I don't want them to go out without enough sleep. Check your ship, and go on."
"Thanks, Uncle Jim." Peter said no more than that, but Bowen knew how he felt.
Peter deliberately tried to sleep for the next ten hours, in spite of his worry about Tumble. The rest of the waiting time he spent eating, resting, and studying maps. When at last it was possible—or rather permissible—to return to the surface, he himself checked the Ion, donned his space suit, and launched the little rocket almost without thinking; the search problem was the only thing that held his mind. For a little while after the start, of course, he did have to think, for navigating a space ship is not quite like driving a car or even an airplane, but he knew the distance he had to go and the speed of the station around the moon, so that it did not take him very long to solve his power-and-direction problem.
He used only one gravity this time, since more would not save much time and would get him tired before he could even start his search, but even with that acceleration it was not long before the Jon was hovering above the moon's surface very close to the point Peter had selected. This was not where the rockets had landed before; as Bowen had said, the sun had set at that point. In that direction was darkness.
This sketch map was copied from the photo maps made at the station when we first approached the moon. I simplified it by leaving out a lot of unimportant details, to make it easier to read.
(1) is where Tumble landed. The arrow shows which way he started out, and the dotted lines show the courses the mathematicians at the station thought he might follow. (2) is where I landed to start the search; the ridge where his trail first appeared is at (3). The arrow there points to the part of the Mountains of Light which could be seen; the closer part of the range is hidden by a bulge in the moon's surface —what a geologist would call a "dome." Tumble says that somewhere near (4) he figured out where he was. You can argue that out with him. The circle at (5) surrounds the two big peaks which Bart and I searched.
The dotted line near the top of the map indicates where the sunset line would have been at the time of the eclipse. The only reason Bart and Dart could see the sun and Earth at that time was that their ships were parked on unusually high ground.
Peter L. Ashburn
The moon cut sharply into the background of stars, with a few bright spots where hilltop
s reached up into the sunlight.
Below him the shadows were long, some reaching completely beyond the sunlit regions and looking like notches in the moon's edge. The surface looked far rougher than it really was, and Peter had a hard time deciding whether any of the areas below were smooth enough to show a trail. He sent the Jon drifting, tail down, several miles in each direction, but at last he realized that he would have to land even to find likely spots to start his search.
He checked his map against the landscape below, found a spot a trifle to the south of the lines which represented—he hoped—Tumble's probable courses, and let the Jon settle slowly. On the ground with his power shut off, he wasted no time; he checked his suit and went out through the air lock. Keeping the sun on his left, he began to walk away from the ship; as he went he examined the ground minutely for tracks. Occasionally, with no real hope of being heard, he sent out a call for the missing boy on his suit radio.
The ground was fairly level, though it had been hard to be sure of that from above. The dust lay everywhere, though it was never more than an inch or two in thickness. Usually when he kicked it, it settled back to the surface at once, like the bow wave from a ship—it looked a little weird at first, though Peter knew that with no air to speak of there was no reason for even the finest dust to float any longer than gravel. Occasionally some of it did stay up a little longer, and at times there were faint bursts of static on his suit radio. But he was too thoroughly occupied with his search to devote any thought to these occurrences, or even to wonder whether they might be connected in any way.
Peter did not keep very close track of how far he went; he returned to the ship twice for food and rest, each time finding his way back easily enough by using his own footprints. There was no risk of the ship's being hidden by darkness. On Earth, in the latitudes covered by the United States, the sun would have sunk below the horizon in a few minutes from the point where the Ion was parked, but on the slowly-turning moon, this close to the pole, the ship would be in sunlight for many hours. Therefore, Peter did not worry about time.
He naturally left the maps on board, and was directing his course by memory, but after several hours on his third trip he felt sure that he must have gone well past any point where Tumble was likely to have been. That raised a rather serious question: had the redhead changed course so sharply that the mathematicians in the station were completely wrong? Or had he kept on going, but traveling on bare rock with no dust covering, at whatever point Peter had crossed his trail? Peter did not think the latter was likely; he had encountered a few slopes whose sides were clear of dust, but in each case he had followed their borders to the end so that he would find any traces which might exist of Tumble's leaving the bare surface.
There was another possibility, of course; Tumble might have kept his direction as long as he could, but still failed to get even as far as Peter now was from the point where he had started. In that case, of course, he should have been able to hear the radio conversations going on during the first landing—and also in that case, he would now be lost in the blackness of the moon's two-week-long night, with the temperature around him dropping close to one hundred Centigrade degrees below zero and no sunlight to operate the air renewing equipment in his suit. His batteries, of course, would operate his heaters and air apparatus for a while, but certainly not for two weeks.
In that connection, a thought suddenly struck Peter, and he spoke into his radio.
"I'm away from the ship and won't be able to hear your answer, but you should be able to hear me, Uncle Jim. How about checking the dark part of the moon around where Tumble landed with infra-red equipment? If he's alive, his suit will certainly be a lot warmer than the rocks around him. I know the observatory in the station has all the equipment you'd need, and it shouldn't take very long.
"I'm going to turn back to the ship and move it to another center as soon as I reach the ridge I can see ahead of me. I'm well past the farthest of the lines on that map, unless I've been traveling far slower than anyone thought Tumble would." He did not wait for an answer, which he would not have been able to hear anyway, but headed on toward the ridge he had mentioned. When he reached it, however, he had to change his plans.
It was higher and steeper than those he had crossed before, and much freer of dust. It was obviously possible to walk along it, in the direction in which Tumble was supposed to be going, and stay on bare rock, and Peter had already found out that staying on bare rock made traveling easier. The dust, he had found, tended to cling to the plastic suits, as dust on Earth did to the plastic "housecleaners" which were so popular with housewives—probably for the same reason, static electricity. On legs and body it meant nothing, for its weight was negligible; but on the supposedly transparent face plate of a helmet it was a serious nuisance, since the stiff gloves of the space suits were not at all suitable for wiping.
It could be taken for granted, therefore, that Tumble would have followed the ridge if he had come this way; in that case he would have left no trail. Peter looked both ways thoughtfully.
To his left, toward the sun, the ridge went on until it was hidden by the near horizon; in the other direction, it seemed to get lower and merge with the more level surface. Peter decided to go right, since there seemed a better chance of finding dust-covered ground there, even though Tumble had presumably been going the other way. His judgement proved right; within two miles the ridge had flattened out almost completely, and once more the patches of dust spread until they covered the whole surface.
Peter had just barely started across what was left of the rise when he found long grooves in the fine powder —grooves which formed a nearly straight line, pointing off toward the dark side of the moon. There was no doubt about the cause, for his own boots had been leaving just such grooves for several hours. In walking under the feeble Lunar gravity, one did not bother to pick up his feet very far; motion was more of a glide, in spite of the clumsiness of a space suit.
"Uncle Jim! I've found the trail—I can't give you the precise position now; I'm going back to the ship, and bring it over here with the maps."
"Don't bother." It was Bart's voice. "We're somewhere above you now, in range I should think. Let me know if you hear me." Peter complied. "All right. Keep broadcasting; I'll home down to you with the radio compass."
Ten minutes later two rockets settled to the top of the ridge, half a mile from the point where Peter was standing; and the next stage of the hunt got under way.
21
MOUNTAINS OF LIGHT
ALL three boys gathered in the Outbound, and held a consultation over the maps. After some argument via radio between Dart and his uncle, they decided where they must be; and it was evident that Tumble had either traveled more slowly than any of the mathematicians had expected, or had not been following Polaris. He had passed closer to the actual pole than anyone had expected. A row of peaks was just visible at the horizon from the control room of Bart's ship, and this was apparently the nearer end of the range whose farther tops formed the Mountains of Light—a fact which Tumble, of course, would have had no way of knowing.
The ridge on which the rockets stood had, the boys supposed, served as a path for Tumble. It was impossible to say just how long ago he had passed; the ground offered only the simple evidence that he had.
"I suppose the only thing to do is go to the other end of this ridge and pick up the trail there," said Bart. "I wonder how far he's likely to have gone? I suppose there's only one way to find out."
"I'm not sure of that," said Peter slowly. The brothers looked at him in surprise.
"What do you mean? How would you check?" asked Bart.
"I think we've been taking too much for granted. We've been supposing that Tumble found he couldn't fly his ship, and went steaming off in search of the Mountains of Light without any particular reason in mind. I know he's a bit hasty at times, but I think we've not been doing him justice.
"For one thing, I think he must have thought out very
carefully the question of whether we would be coming to look for him or not. We know he doesn't trust us fully, but if he had decided we weren't coming he'd have stayed in his ship)—at least, I would expect him to. He'd live longer there.
"If he expected us, then there's some reason behind his going where he did........"
"I know," interrupted Dart. "We've already supposed that he would be heading for the Mountains of Light —I don't see that it matters if he was going there because he wanted to see them, or he needed constant sunlight to keep his air supply up, or figured we'd be most likely to find him there. The important thing is that he didn't start out for those mountains, but in a direction which would take him miles to their left; and we've just found that he held the direction pretty well —at least, up to here he hadn't changed it enough to hit the mountains."
"Just the same, I think he's somewhere in that range right now."
"Wha-a-a-t? Are you sure your brains didn't get dried out along with your maps a while back?"
"All right, you tell me why we haven't heard a call from him—or better, why the station hasn't. He can't possibly be out of range just by distance; there's something in the way. Look at this map; in the direction the mathematicians thought he was traveling, he might be in this other range here." He pointed out the one he meant. "The first catch to this is that if those mountains are the ones which were blocking his transmission when we first arrived, he traveled a good eighty miles in less than fifteen hours."
"He wouldn't have had to get that far to be blocked from us; the horizon is pretty near on the moon."
"From us, yes; but the horizon wouldn't have shielded his waves from the station. He'd have to be in a pretty narrow valley somewhere for that."