“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.”
The Shervah, unfortunately, followed the suggestion, and like her friend found the sight interesting. The drifting, shimmering, writhing blobs of fluid were indeed beautiful. Lacking cameras, they alternated with each other trying to describe what they saw to Jenny and the others. Not quite all their attention was thus employed—both were conscious that the “drops” were spreading farther and farther from the original fall and closer and closer to the robot, in their random wanderings—but neither was thinking of danger for the moment. Probably neither would have been able to foresee its details even with full attention.
Quite abruptly, the robot’s descent stopped, or seemed to. Carol reached for the control keys, while Molly swept her light around to see whether they had reached a solid cave floor or a lake. She saw neither, and before Carol could finish her key work the descent resumed. The Human began to report the event to the others, while her companion swiftly considered possibilities. A likely one occurred to her immediately. A large drop might have drifted below them temporarily and been interpreted by the robot’s sensor as ground. She suggested this to Molly, who interrupted her partially completed report with a brief “Wait a minute,” and both turned their lights downward to check the possibility.
It seemed likely enough; there was a blob of ammonia only a meter or two below, whose motion suggested that it might have been right under them a few seconds earlier. Molly nodded and was about to resume her call to the others when Carol called her attention to another.
“Hold it; we’ll check. There’s one that should drift under us in a few seconds—half a minute, maybe. We’ll be nearly down to it by then; let’s see if the robot does the same thing. If it does, we’ll know, and can move out farther from this—would you call it ’spray’?”
“All right. Are you following, up there?”
“More or less,” Joe replied. “Update us when you can; I get the impression you’re busy.”
“Thanks. A minute or so,” replied Carol. “We have a check to make on what your height sensor responds to—yes. There. We are stopping again, Molly. Shall we get away from here right away, or—we’d better move; staying won’t tell us anything more.” She reached again for the keys but was too late.
Ammonia is less polar than water. It therefore has a lower surface tension and tends to wet a given surface less readily. The latter quality should have helped when a smallish, half-meter mass of the liquid touched Carol’s shoulder, but the former was enough. The drop did not hold its shape but spread out, covering her helmet almost at once. She was not using her sight on the keys, naturally, but having that sense blocked was quite enough to distract her. She failed to key the new command.
She knew what had happened, of course.
“Molly! Get this thing off me!”
The Human was equally quick at seeing the trouble, but this was not quite the same as knowing what to do about it. Nothing remotely resembling a large sponge was on hand. Gloves, Human or Shervah, were quite inadequate wiping tools. The laser sampling cutters were as likely to boil the armor as the ammonia. It was several seconds before Molly thought of using the heat output from her armor’s refrigerating system, and many more before she could get herself into a position to apply this usefully. By this time, Charley was asking frantically what the trouble was.
Molly was too busy at what amounted to a free-fall dance to be able to tell him, but Carol, who could do nothing but hang onto the robot and keep as motionless as possible, made it clear. Before she was finished, Joe made one of his rare interruptions.
“Carol or Molly! Close the access door to the robot’s keyboard, if you haven’t already!”
“Gravdh! M’Kevvitch!” No one asked for translation as Carol’s glove slapped at the small panel. “Got it. But won’t ammonia leak in through those pressure-sensing openings all over it?”
“I didn’t overlook quite everything. They seal against liquids. I’ve heard of rain. If you have the port shut, it will be liquid-tight.”
“But we’re still in the spray area. More drops could hit us any moment. With the port shut, I can’t move us out.”
“When Molly gets you dry, you’ll have to look around and try to spot a moment when nothing is going to get to you, and do a quick job of…”
“Another drop!” cut in Molly. “I’m falling behind. Who’d have thought we’d need bath towels in this operation?”
“Can you wave your arms, or something, to make air current that will move them away?” asked Charley.
“I’m trying. It works for the little ones, but I can’t see in all directions at once, and Carol’s helmet isn’t clear yet so she can’t either.”
“But why can’t she see through ammonia?” Charley asked almost plaintively. “It’s transparent!”
“It’s ripply!” snapped the Shervah.
Charley once again was visualizing the Human’s battle with Enigma and wondering how many more tests there would be. Why had Molly put herself in the position where she, rather than one of the others, was having to take the physical action against the weird little world’s environment, instead of staying in the boat or the tent and letting the others act as well as think? Maybe the presumptive Faculty policy against letting students get into really dangerous situations was operating, but that couldn’t be the whole story. Carol was down there, too, facing the same risks, apparently.
And why had Molly come up with the idea of using her armor’s heat pump to get rid of the ammonia, instead of letting Carol pass the test herself? The Kantrick, positive from the beginning that they were repeating a laboratory exercise that had been done thousands of times before, almost as certain that the Human was the Faculty member responsible for rating them, was beginning to have doubts about her as a teacher.
Molly, at the moment, was not even a student. She was concerned with keeping the two of them alive, which seemed to mean finding the ideal time sharing between fending off more drops of ammonia and keeping the radiation from her armor’s heat pump directed at Carol’s helmet. Once the Shervah could see out, her side-placed, independently movable eyes could do a far better job than Molly’s stereoscopic equipment at watching all directions for more of the amoebalike blobs.
Carol was waiting, and worrying. The robot was sealed against the ammonia, but had she done the job in time? She had been thrashing around thoughtlessly for a moment or two, and might have flung smaller drops of the stuff in any direction. The machine was safe enough in one sense—it had breakers that would shut down any part affected by short or sneak circuits. A fusion unit melt or blow was a possibility that not even laboratory experience brought to anyone’s mind; the devices were as ubiquitous to all their cultures, both in School and on their home planets, as ballpoint pens had been to the Human’s ancestors. They simply didn’t think of them as dangerous under ordinary conditions—Molly’s fear about the robot’s driving into the cave wall, earlier in her adventure, had been a special case, like a child falling while carrying a pen.