Hal Clement - Still River

“It could still pack momentum,” remarked the Nethneen. “Be careful.”

“Don’t worry. The wind around it is plenty of warning, slow as the waterfall looks.”

“Which way is the wind? Any guidance?” asked Charley.

" ’Fraid not,” replied the Human. “Random stuff; eddies set up by the moving water. We’re holding motionless, if the inertial guidance can be trusted, and can feel this-way-that-way gusts trying to knock us off the robot.”

“Then what will you do? Come back the same way you’ve been traveling?”

“Where would that get us? And when?”

“Closer to the surface, at least.”

“Not good enough. All we know about the area around the original cave is your information that there seem to be no other surface openings near it. At least it seems sensible to be heading somewhere else—maybe toward one of the places you or Jenny have found. Heading down a river has something to be said for it, by itself; if any of you find one, doing the same is probably the best remaining chance of getting us together.”

“If rivers tend to converge underground the way they do on a surface,” Charley remarked.

“Do your own theorizing about that; I don’t want to!” snapped the Shervah.

“You could be heading straight away from the region we’re mapping.”

“Maybe,” agreed Molly. “This robot knows somewhere inside its crystal cerebrum, I suppose, but we can’t ask it. Or maybe—Carrie, you’ve been using the inertial system telling this thing which way to go. It must have some reference direction of its own. If we let it sit quietly on a solid surface, how long would it take to tell itself, if it doesn’t know already, which way and how fast this planet is rotating? Personally I’d guess about five minutes, but you know better than I do, probably.”

“I’m not sure I do, but that seems a reasonable guess. Joe, I never knew—did you build the sensors in Classroom’s shop, or use standard ready-made ones?”

“Oh, I built them, of course. Slowly as Enigma rotates, five minutes will change attitude quite enough to measure. A good thought, Molly.”

“Then we’ll land beside the waterfall and let this thing decide which way is north, and then head in that general direction; that’s where you two have been finding your wind vents, isn’t it?”

“Yes,” replied the Rimmore. “Should we bother to look for more?”

“Of course. Keep on mapping toward us, if the storm will let you.”

“I have another suggestion” came Charley’s voice.

“What is it, Charley?” Molly answered quickly, gesturing her small companion to silence.

“I propose to go underground at the nearest entrance I’ve found; perhaps Jenny might do the same thing, but if she wants to do that she should use one of the places near where I do.”

“Why?” asked Carol impatiently, ignoring Molly’s obvious wishes.

“You can program the robot to stop after it has gone a certain distance in a certain direction—it can keep track of all components of its travel, no matter how irregular its actual path. Even if it won’t give any other signal, you can find out when you’re close to this area, which is…” he paused to interpret instruments “—three hundred fifty-one kilometers distant and twenty grads right of north from the hole you two went inside by. Just arrange for it to go that far in that direction and stop. It won’t be exact, obviously, but it will put you somewhere in this neighborhood. While you’re making that trip, I, and Jenny if she wants, can be mapping the caverns under this area, within whatever radius seems smart, and as deep as we have time for. We will, of course, file the map in the boat’s computer—no, we’ll be out of electromagnetic touch once we’re very far underground, but our own machines have enough capacity to record the planet, probably.

“Once you two know you’re in the area, you can start examining it in detail, moving around as seems good to you, and describing it carefully. Sooner or later we’ll find a match with one of our maps.”

“Beautiful!” Molly made no attempt to hide her enthusiasm.

Carol didn’t feel as happy, considering the source of the idea, but could not deny that it seemed a good one. “I’m not sure it’s better than staying with the river, but it has possibilities,” she admitted.

“There was a good windy cave only fifteen kilometers from here,” Charley resumed. “That will make it three hundred sixty kilometers and almost exactly north for your robot setting, Carol. Are you going to come over and map, too, Jenny?”

“Yes, by all means. Let’s see—my unit has copied from yours, so the maps are joined—there’s another vent only a dozen kilometers from yours, just about east—that will make its distance about the same for Carol and Molly, and we’ll be a broader target laterally. I’ll start at that one, and we’ll try to make our underground maps join up as quickly as possible at as many depths as we can.”

“Fine.” The Kantrick was in top spirits again. “I’m at the vent, and going underground. At least I’ll be out of the glare of this murderous star.” He shifted to private channel. “Was that the right idea, Molly?”

The Human couldn’t quite see the point, either of the question itself or of his making it private, but she followed his lead. “There are probably hundreds, almost certainly dozens, of workable ideas. This seems a good one. There’s only one thing that would make one ’right’.”

“Is it the one one of us was supposed to have?”

“Supposed by whom? I was hoping someone would think of something to get us out of this mess, and I’m happier than I’ve been for—it seems like weeks. Thanks, Charley.”

“Molly.” It was Carol, on general channel. The larger woman looked inquiringly at her. “I’d like to go fast, once we know which way to go, but I don’t want to sail at full clip through an empty cave with no idea of when the far wall may come up. Shouldn’t we find the bottom, if only to keep ourselves conscious of how fast we’re going and a little more alert to what may be ahead?”

“Probably we should. But how fast do we dare go down?”

“That’s no problem. The robot can sense its own height even if it can’t tell us, and I can key it to stop on a downward trip before it hits anything.” Carol refrained from mentioning how nice it would have been had the machine possessed similar horizontal sensing capacities. “As soon as we’re oriented we’ll move out far enough from the fall to feel safe, and I’ll set up a fastest-downward.”

“What if we’re over another lake? This waterfall—excuse me, you know what I mean—must stop somewhere, and…”

“It will read that as a surface. Don’t worry. Even if we splash, we’re in armor.”

Minutes later, the two were once more descending through Enigma’s darkness. Molly had set her light to the narrowest, brightest beam possible without hurting Carol’s eyes and was keeping track of the falling liquid a couple of hundred meters away, while the Shervah swept hers in the opposite direction and occasionally downward, using a broader focus.

“We’ll have to be ready to move farther from the fall,” the Human reported after a minute or two. “I suppose this is what happens to real water under decent gravity, too, but I’ve just never observed the detail. The fall reaches terminal velocity for this gravity and air density, which is pretty slow, and starts to break up into big drops, and those are blowing around randomly. I suppose they correspond to the spray under a real waterfall.”

“How big are the drops?” Joe asked with interest.

“The smallest I see from here are a centimeter or two. They range up to blobs of a couple of meters, changing shape and orientation as they fall—if you can call that drift a fall. We’re going down faster than all but the very biggest, so I haven’t been able to follow any one of them for very long. They’re pretty, Carol; have a look. I’ll cut my light for a moment; yours should reach that far, with your eyesight.”