“A point that I shouldn’t have had to have pushed at me, since I am very used to weather,” Molly conceded. “All right, then. Charley, like us, is a long way from the center, and his river is vanishing. Ours will probably do the same before very long, unless it’s a much bigger river, or meets a much bigger one. When that happens, we either wait for your mappers to find us, or go back to traveling upwind when there’s a horizontal component to follow and straight down when there isn’t. Incidentally, Carrie, we’d better set this machine on solid rock again soon and let its inertial system have another feel for the planet’s axis. We could have come a long way horizontally since it last had a chance to tell which way is up.” “Good point.”
“How about the size of your river?” asked the Kantrick. “Does it seem to be shrinking at all?”
“We have no way to tell,” replied Molly. “It’s been a long time since we could see all of it at once. It should guide us downhill for a while yet; it’s certainly pretty big.”
“Mine’s just a trickle now, with occasional drops up to brain-dome size being picked up by the wind and carried back upstream evaporating as they go. Several of them have hit my window—I see what you mean about what they do to the seeing, Carol. I have to slow down, or even stop, until they dry up. I’ll be able to go faster when the river vanishes entirely.”
“If you can decide which way to go.” “Upwind, of course. That must be coming from the central hollow, in this hemisphere.” “I hope you’re right.”
“I’m not worried. The main nuisance will be finding the wind direction. These mapping robots aren’t built to sense it; I’ll have to cut power every now and then and see where I get blown, if there’s nothing else loose to show me. Score a point for low gravity.”
Two, Molly thought, but kept the thought carefully to herself. Aloud she pointed out, “If you have rope with you, you can make some sort of wind flag. You’d still have to stop to use it, but it might be better than letting yourself get blown away.”
“I meant the boat, not myself; I had no intention Of emerging. Your flag idea is excellent—though I’ll have to get out to set that up. I’ll do it as soon as I figure out a way to hang it on some sort of support away from the mapper’s hull. I may as well try to get an undisturbed wind.”
Joe made no comment to any of this. For once, he did not feel guilty at having omitted wind sensors from the mappers; there was no obvious reason why they should have been needed. Actually, he was paying little attention to the Kantrick at the moment, because his own mapper was getting very close to the inner surface. He would have to decide very soon which mapped passage to follow himself and what region of the growing model to favor in guiding his small sensors.
The disc was now a set of tentacles probing into Enigma’s crust once more. As the signal from any mapper advancing along a passage became weakened, another machine automatically positioned itself to relay and followed the same tunnel. The second would be followed by a third and still others as needed; Joe’s problem was to decide how many tunnels to check at a time. The more he was mapping, the shorter the distance in any one that could be covered before running out of relays. There was no way he could think of to establish the perfect balance between reasonable probability of including the right direction and—
And what? Why was he worrying about time? The women could survive for weeks yet, as long as their energy source remained available, and there seemed little chance of another slip in that direction. Of course, research involves the unexpected.
Such as the realization that there had been changes over most of his recently mapped surface, he suddenly saw; and that less than half of the small mappers seemed now to be contributing signals to the model. He still couldn’t spot individual sources, of course, but he could estimate well enough how many machines were committed to each tunnel.
After a little thought, he reworked his program to indicate by color change which passages were still increasing in length on his model. The picture was a complicated, bushlike structure, rather hard to appreciate in full, but it quickly verified his suspicion. Fully half the branches of the bush had ceased to grow. Something was stopping his mappers.
Chapter Twenty-Three
Of Course I Can Get A Spectrum
Molly was more certain than ever that Joe could feel emotion as his latest report came through her translator.
“How do you know they’re missing?” She put the question as calmly as she could, remembering how the Nethneen had been so careful of her own feelings earlier. “I thought you couldn’t identify their individual signals.” “I can’t. That’s why I was so slow realizing what was happening. Several of the branches—the passages—in the present section of the model have simply stopped growing. Since others were extending normally and the pattern is fairly complex already, the frozen ones weren’t obvious without careful examination. Carol, with her memory, might have spotted the situation more quickly; I could not.” “Couldn’t the passages simply have reached dead ends?” “That would have been indicated; a good many have been. Some things I did foresee clearly enough to program. I cannot see any interpretation for this other than a stoppage of incoming signals, though the fact that the height of the surface over much of the mapped area has changed slightly—a centimeter or two—may also be relevant. I am of course heading for the nearest of the frozen branches as quickly as possible, to see for myself what’s happened.”
Molly just managed to restrain a comment about possible danger. Joe would be careful, of course, but he could no more ignore the situation than could Carol or, basically, than Molly herself. It was Carol who actually spoke, and it was some time before Molly realized that the Shervah was also giving prime thought to analyzing the danger—the danger to the mappers, of course.
“Joe, don’t go too fast. Please examine and describe as carefully as you can the nature of the rock, or whatever may form the walls of the passages you traverse. If you have time to stop and take samples, or even do a quick spectral analysis, do it.”
“You have an idea of what may have happened?”
“Not a full scenario. A possible backdrop. Get the data to me, please.”
“I will. I am just approaching the surface. I told you earlier that this area was much smoother, according to the radar model, between the actual tunnel openings than it is farther from the poles. I have not seen such material before on my own world. As I approach, the smoothness starts to show a pattern of cracks outlining polygons of usually five or six sides, anywhere from four or five centimeters across to eight or ten times that size, the edges rather curled up—pardon the word—away from the surface and toward Enigma’s interior.” One of Carol’s eyes rolled toward her companion; Molly caught the glance and nodded.
The Shervah interjected a question. “Is that concavity true of all the polygons, or are some of them flatter, rougher, and set farther from the surface—as though a curved plate such as you are describing had been removed?” Joe gave no answer for several seconds; Carol and Molly waited patiently, knowing that he must be making a careful search for the sort of feature she had suggested. Charley’s voice started to sound, and ceased again before he had completed a word.