Eyeball Vectors
(1992)*
Hal Clement

	The background was dark to both Erthumoi and Cephallonians fifty meters down. Habranha's sun, an M-type dwarf, had little of the blue and green light that might have penetrated that far, and here at The Cataract was usually hidden by clouds anyway. Frequent specks and threads of luminous plankton appeared in front of the travelers and fell quickly behind, but Janice had only one interest in these. Even the rare explosive ones were usually too small to be dangerous, but they did provide a little warning of Thrasher's maneuvers.

	The Cephallonian was avoiding the larger plants with his usual grace, now swerving sharply one way or the other, now diving or rising as suddenly. He could trust most animals to dodge him. The carrier in which Janice rode, on the right side of his suit, was full of water to make it match the bulk and drag-of the oxygen tanks on his left, so she was not being thrown around; but for the first time in years she was feeling motion sickness. If she couldn't have seen what was coming, it would have been much worse. Happily the vertical currents in particular were outlined most of the time by the glowing dots, lines, and patches of Habranha's more electric life forms.

	She was not sure what nausea could do when one's body cavities and breathing passages were full of diving fluid, and she didn't want to find out. Eating took care enough, and vomiting might be really dangerous. The reflexes that normally let only gas into the human windpipe had had to be blocked to let her use the pressure-guarding liquid. No one had known how far down the Pupil Study Group's work might lead it into the little world's ocean, but someone had to be ready for a deep dive. It was merely funny that the someone had to be an Erthuma rather than a Cephallonian. The cetaceoids had personal limits of a few kilometers, and their technology had never produced anything like the pressure fluid.

	Janice tried to keep her mind off the possibilities by conversation. This took much attention, since it had to be by code; human vocal cords don't work in liquid.

	"Can you spot them yet, Thrash?" she keyed.

	"Not certainly," replied the Cephallonian. He could speak normally, since there was water inside his suit as well as outside, and the translator could handle sounds in both water and air. "There's something which seems big enough ahead of us and, I think, at the surface, but I can't make it out clearly. Too many verticals and density variants around to distort the sound, and too much suspended, floating, and swimming junk besides. It does seem to have edge behavior like the raft, though; surface waves are damped as they approach it, if I'm interpreting correctly. That could be the deck."

	Janice didn't want to hear about vertical currents. They were the main cause of her discomfort. An ocean should be quiet near the substellar point of a tide-locked planet, where only simple evaporation ought to be taking place, but Habranha had its own ideas about practically everything. Very little on this world was simple.

	She and her husband had learned this the hard way earlier, in the Sclera section near the edge of the dark hemisphere. The ice there was water, relatively pure except for trapped silicate dust. Ammonia stayed mostly in liquid solution at that low temperature; near the dark rim, an Erthuma could breathe the air without too much discomfort—for a while, as it also contained traces of hydrogen cyanide. The planet, however, was largely ice, like Titan or Triton in the Solarian system; and since it was close enough to its small sun for the ice to melt on one hemisphere, there was a very deep ocean made principally of water but holding much dissolved ammonia and suspended solids such as silicate grains, various phases of water ice, and an enormous variety of biological material. Warm water could not be depended upon to rise, or cold to sink; ammonia and other content could rule otherwise. An iceberg might be carried up or down in a density current and change phase as it reached a pressure boundary, either abruptly or at some unpredictable later time when it finally yielded to internal stresses, shattering to fragments or to dust and releasing or absorbing enough heat to invalidate the most detailed calculations. The weird behavior in the ocean was reflected in the overlying atmosphere; native Habranhan meteorologists were far more skillful than the visiting aliens who were sometimes arrogant enough to try to teach them their own art. They still, however, had poorer prediction scores than did those aliens on their own worlds. Hence the arrogance.

	Far from the ice hemisphere, past The Iris, the ring-shaped floating continent of merged icebergs, and on to the center of The Pupil, the ice-free sunward ocean, it seemed as though things should be simpler. They weren't. Janice Cedar, her husband Hugh, and the two Cephallonians who formed with them the Pupil Study Group knew now they were all in trouble, though they had not yet accepted that they were doomed.

	"How far?" she asked. Some seconds passed before Thrasher's voice came from the translator. "I can't be sure. If it's really the raft, then I'd say about twenty kilometers. I can't get any of my own echoes, though. All I'm spotting seems to be wave sounds from the source, so distance is guesswork. That's why I think it's at the surface, and can hope it's what we want. Why don't you try calling? Your low-frequency stuff gets through better, and an answer would give us travel time. Hugh'll be listening, I expect."

	If he weren't, the woman thought, it wouldn't matter;

	The Box will be. And I hope it isn't really twenty kilometers; the tracker says it should be seventeen point seven one, and even this turbulence shouldn't have thrown it that badly off. She switched to her outside transducer and tapped out a here-we-are. The Box's response, at Thrasher's distance guess, should take about fifty-five seconds, but one would have to allow a bit more for human reaction and decision time if Hugh were involved.

	After a minute and a half, the cetaceoid voiced the more pessimistic interpretation. "Not the right target, I guess. I hope you're not getting worried."

	"Should I be?"

	"Well, frankly, if that's not the raft, I have no idea which way we should be going. I suppose we can trust your tracker? It said we should head this way when we came back up—or at least you told me it did when I got my senses back. You seemed pretty sure of it. That was as rough a dive as I've ever made, though, and even this leg of the swim has been pretty snaky."

	"It isn't a planetary range instrument, but it should be good within a few centimeters in what we've logged so far. The raft should be just under eighteen kilos, in the direction we're heading right now—or were half a second ago." Thrasher had swerved again to avoid a larger than usual patch of luminous weed. It took him several seconds more to come up with an answer. He might have been concerned with the weed, a type that was normally highly charged, or with something entirely different.

	"Then why no response to your call?"

	"Hugh and The Box could both be busy, and Splasher probably wouldn't have heard it even if she's there. She could be away for any of a hundred reasons."

	"But you're not worried?"

	Janice repeated her evasive counter. "Should I be?"

	"Well, I'm getting a little tired. Fighting turbulence is work. It's lucky the downs are denser so our buoyancy helps, and the ups less dense with the same result."

	"That's not luck. It's laws of physics."

	"I know. But isn't it lucky the laws are on our side?" The woman might have answered this if she had had the use of her voice, since several responses occurred to her at once. However, spelling out philosophy via code key seemed hardly worth the trouble. The Cephallonian paused only briefly for an answer, and gossiped on. "Can't you imagine what these verticals would be like in decent gravity?"

	Janice could, but didn't want to. Decent gravity for either of them was roughly five times that at Habranha's surface, and convection currents are driven by gravity as well as density difference. Also, she was getting just a little worried. If Thrasher were actually tired, they could really be in trouble, something more immediate than the basic problem of the whole group. Swimming even two or three kilometers alone would take her hours, and the thought of towing her huge companion would have been funny if it weren't so grim. She was of fairly standard Erthuma-female proportions, a hundred and fifty-four centimeters standing height by forty-five kilograms of mass. Thrasher, while much better streamlined hydrodynamically, had over ten times her mass, and even adjusted to neutral or slightly positive buoyancy would have represented a hopeless task for towing.

	Deserting him never occurred to her.

	Her own buoyancy was set slightly positive, of course. Her companion's should be even more so now that a lot of his oxygen must have been used. Habranha's partial pressure of the gas was high by Erthuma standards, allowing Hugh and Janice to make do with filters when out of water, but not by Cephallonian ones, though the swimmers could survive at low activity without extra supplies.

	She and Thrasher would float, and could therefore breathe, if their strength gave out. Maybe Splasher would find them eventually, but maybe she wouldn't, and away from the raft there was the problem of food. Worrying, of course, was never much use, but planning might be in order.

	Her suit would supply her for a while, but it wasn't a real full-recycling exploration unit. Thrasher had only the stored food and oxygen he had brought along, and with his size and metabolism those would go quickly. Neither could eat the local life, not even the sort that used DNA and ATP, and neither was carrying the fermenting units which could turn Habranhan biomass of that kind into edible "cheese." There were four of these back on the raft, two for human and two for Cephallonian use, but none was small enough for even Thrasher to tow conveniently.

	So they had to get back to the raft reasonably soon, and their only guide was her tracker. The target Thrasher was hearing had better be the raft, and its failure to respond and the distance discrepancy had better not mean trouble there. Of course, her companion had felt unsure of his distance estimate, she reminded herself; but why the silence?

	She keyed out another signal and, a kilometer or so farther on, still another. Thrasher said nothing at either lack of response, but was swimming more slowly. This was a comfort in one way, as her stomach quieted down, but not in the other. How long could the old whale last?

	There is no point in worrying, Janice told herself firmly. We can float for days. Maybe we'd better surface now, and just wait. Of course, the surface will be rougher still, and the motions a lot less predictable, but let's not think of that; we're facing a practical problem. Splasher is bound to come looking, but of course she won't have tracking data, and when we started the test dive The Box had a clear image for only a couple of kilometers' radius. We left the raft straight downward, with no idea of what lateral currents we might meet. She'd have to make a full circle search starting from the raft, and she couldn't assume we'd have been able to surface. She'd have a hemisphere, not a circle, to explore.

	Not so good. We'd better keep going. The closer we are when Thrasher gives out, the smaller the search volume will be, at least.

	That is, of course, if we are getting closer.

	"It keeps sounding more and more like the raft," her friend remarked at this point.

	"Can you make it?" she keyed.

	"Eventually. I wonder why they haven't answered you?"

	The Erthuma still had no explanation to offer, but took the query as a hint to try again. She was getting just a little uneasy about this; each lack of answer made it that much harder not to worry. She had just touched the keypad when Hugh's voice came through the transducer.

	"Hi, there. How deep did you get? Any problems?"

	Again his loving wife found the code frustrating. There were so many ways she'd have loved to reply to that one—

	She settled for "Any trouble there? You didn't answer the here-we-are." She couldn't even underline the there. Her husband could have read a lot from her voice, but she didn't have a voice. Now the darling idiot was assuming that the dive had been uneventful, since she hadn't answered his question.

	"Sorry. We've been busy. The Box has been making more sense out of its echo data, and has a practically realtime chart of the currents for nearly thirty kilometers horizontally and over three down. They're really something, aren't they? We spotted you ten minutes ago, once The Box was able to allow for all the refraction and scattering of sound, and it could tell you were on the way back, but we weren't in time to see you at depth. How far down did you get? Any useful material? Can we ever get out of here?"

	"Of course you weren't listening, since you could see us."

	"That's right." Hugh suddenly seemed to sense a touch of emotion even in the code buzzes. "You are all right, aren't you?"

	"Thrasher's wearing out. Deep currents even worse. He got more determined to go on the worse they got. I had to use The Order."

	"You didn't tell me that!" the Cephallonian cut in.

	"I was afraid to after you woke up. I thought you'd have guessed. How's your memory?"

	"Well ..." The translator paused. "I see. Yes, I should have figured that out. Was I really bad?"

	A simple yes seemed easier than "You were starting to talk to the currents as though they were personal enemies, we were half a kilo deeper than we had planned for the test limit, and you were swearing by something that wouldn't translate that you weren't going to be thwarted and frustrated by something that wouldn't translate either," so yes was all Janice keyed.

	"Splasher says she bets he's starving," Hugh cut in.

	Thrasher also limited himself to a simple yes, more because the response delay was still nearly forty seconds than because he couldn't have expressed himself more forcibly.

	"She's on the way with food, or will be by the time this gets to you. The Box will guide her; she can't hear you yet herself. Better hold off reporting until she's close enough not to need help. Relax if you feel like it."

	"We'll surface," Thrasher returned. "It'll be easier to eat with the suit open."

	"I didn't think." The man's voice, clearly contrite, partly overlapped the swimmer's. "I let her go off with no human food. Do you need any, Jan? Surely you're not out."

	"All right here. Don't worry." She was rather hungry, now that she thought of it and they had stopped charging through verticals, but there was a good supply of the tapelike recycled stuff in her processor. She worked the control that began delivering the strip to her mouth, and bit off a few lengths. It was fibrous and hard to chew by design, and by the time she had dealt with it satisfactorily Splasher and her companion were able to talk directly to each other. Practically unburdened except by her environment suit and its oxygen tanks, the female Cephallonian had an impressive turn of speed.

	"I can't get echoes from you yet, but I can hear your voice. Keep talking, sweetfish."

	"Sure. We're going up so I can open up and eat properly. I hope you brought more than concentrate. I'm starved ..." Thrasher kept talking as ordered, but it became mere babble to Janice.

	"Sorry, I wanted to travel fast. There'll be a real feast back at the raft, if you can still stand cheese. You'd have trouble enjoying it now, anyway; it's been stormy as ever with at least a dozen spouts since you dived, and it's just as rough now, so don't be too casual about opening your hood away from the raft. I think I can get your echo now."

	"Likely. I'm spotting yours, and mine should be stronger with the equipment and Janice. We're only ten meters down now—you're right, the waves are still—" The translator gave its burping sign for no-symbol-equivalent, which did not surprise Janice; any Cephallonian language has more words for wave conditions than clothing stylists have for colors. As far as she was concerned, the appropriate word was "terrible"; even at ten meters she was starting to feel the surface roughness. Maybe she shouldn't have eaten, after all. She knew what the top was like; she had lived enough of it in the last few days. In theory, wind had a long reach—hundreds of kilometers from The Iris, which bore the Habranhan cities and farms, to cloudy Cataract in the strong evaporation zone under the sun. Waves should reasonably have been long and regular. Coriolis effects had to be negligible; not only were they practically at the little world's equator, but its rotation period was over three weeks.

	Even here, however, chaos reigned. A patch of ocean would grow just slightly warmer than its surroundings, either from sunlight or from biological effects. Ammonia would become correspondingly less soluble and escape into the atmosphere, which would drop accordingly in density and start a strong updraft. The water would of course grow denser and settle. Wind and surface flows would race toward the spot with essentially no inertial deflection until the final moments and even then in an unpredictable direction. There might be a waterspout, a whirlpool, or both; neighboring spouts or eddies might attract or repel each other; whatever happened, no wind or waves got very far undisturbed in this region. Regularity in either was unknown. Farther away from the evaporation center, of course, there was an effective long reach. Long, high waves did build up across The Pupil, focusing on The Cataract, and found their way into the chaotic mass of rocking, swirling local storm centers where even the winged Habras didn't try to fly. Once there, though, they merely complicated the local chop.

	Janice began to doubt that the surface was for her. Not just now. Not just in a suit, or even riding the massive Thrasher. The raft was bad enough.

	She tried valiantly to concentrate on the Cephallonians' conversation, but with less and less success as they neared the heaving surface.

	She shouldn't have thought of that participle.

	"Thrasher," she buzzed, "I'll have to go back down. I can't take the motion—I'll explain why later, or you can ask Hugh. I'll be swimming toward the raft; you two can catch me when you've eaten." Without waiting for an answer she opened the carrier in which she had been riding, emerged, and headed downward. It was rather hard work, but not impossible. The temptation to reduce buoyancy was easy to resist when one knew that the darkness extended five hundred kilometers that way before anything except perhaps a wandering iceberg on the verge of explosive shattering would stop a sinking body. She had no intention of sleeping, and expected no accidents that might knock her out, but common sense insisted on positive lift.

	Waves or no waves, she would be easier to find and possible to reach on the surface.

	She keyed a brief message to Hugh, telling her plans.

	"Why?" came his reasonable question. "Thrasher can bring you here in a few minutes."

	"Surface rough. Stomach."

	"Oh. All right. The Box will keep track of you, and I'll have the two pick you up when Thrasher's eaten. I hope—" He fell silent.

	"What?" There was still a long wait for his answer.

	"The raft isn't exactly steady, either. Maybe when you get here you'd better get rid of the diving juice and let me take over the deep work. I don't get queasy."

	"We'll see." Janice had no intention of giving up what promised to be the interesting part of the trip, but arguing by code was far too much nuisance.

	Having Hugh come with her into the depths, as he had before during the Sclera investigation, would of course be different. In fact, it seemed a very good idea, and there was enough reserve diving fluid to allow it. Maybe the need for a surface monitor could be ducked somehow. If not, however, Janice Wind Cedar would not be filling that job. It would be her beloved husband Hugh who stayed on deck watching instruments, regardless of how protective he might feel.

	She was still firmly of this opinion, tired as she was getting, when the Cephallonians caught up with her. She resumed her place in Thrasher's carrier without comment, and in half an hour they were at the raft.

	This was simply a resting tank for the swimmers and support deck for equipment. A large framework outlined a volume of water shallow enough so that they could keep their blow-slits near the surface and breathe occasionally with minimum effort. Some sort of streamlining was achieved by covering the sides with polymer sheeting. From below the surface, the main body of the structure looked a little like a canoe submerged to the gunwales and with the open stern cut off flat. Decks of stiffer polymer formed the tank's bottom and a rim some five meters wide all around at the waterline. A low shelter stood on this for the convenience of the Erthumoi. Between this cabin and the nearest edge of the tank was a roughly cubical structure some three-quarters of a meter on each edge; why this was called The Box was obvious. Near this was a compressor and filter system to charge oxygen tanks, and inside the resting place near it, mostly under water, a rack of high-pressure gas cylinders. Half a dozen smaller structures, sheltered like The Box from rain and spray, were scattered around the edge of the tank, accessible to both Erthumoi and Cephallonians, to house the research equipment and fermenters.

	Floats of polymer foam were attached at scores of seemingly random points all over the structure—under the deck, at its edges, and around and under the tank. No one of these was highly buoyant, since the designers did not want wind to have much of a grip on the craft, but there were enough of them to satisfy the firmest believer in the value of redundance. A dozen hydro-jets were mounted on as many of the floats, allowing the whole unit to be maneuvered rather clumsily. No one had studied the currents closely enough to foresee the need for more. The winged Habranhans had reported that the aerial storms in The Cataract were violent, but no one seemed to know much about the sea.

	Someone had made a casual estimate of centripetal currents based on calculated evaporation rates, and powered the raft to move at twice their speed. This was why the Pupil Study Group was in trouble. Evaporation had been calculated simply from cloud observations made from space. No one had computed the amount of ocean that sank from ammonia loss and thus created more inbound current. In fact, the surface flow toward the planet's sunward pole reached a speed much greater than the raft's thrusters could override. None of the four living explorers had paid enough attention to the trackers to notice this on the inward trip, and no one had told The Box to watch out for such matters. Winds feeding into the same zone reached speeds five or six times as great as the ocean currents, resulting in spectacular waves; but the raft had very little structure above the surface and no one had really worried about air motion until they reached the really chaotic region almost under the sun.

	One does not use or even carry radio transmitters on Habranha, since they interfere with native speech. There was no neutrino set on the raft, so they could reach nothing off the surface. It was wildly unlikely that they could be spotted optically from orbit against a stormy ocean background even if The Cataract's cloud cover should happen to open briefly, and even more unlikely that a flying native would pass anywhere near. Habranhan researchers concentrated on the Sclera region, the low-sun rim of their small world, where grew the icebergs making up for the ever-melting warm edge of The Iris. The stormy hot pole was not only a dangerous flying area, but promised little useful knowledge. The net result was four explorers entirely on their own.

	Hugh was summarizing. His wife would have been better at it, but code was too slow.

	"As far as food goes, the fermenters will keep us alive indefinitely, or until we let something into them that poisons their pseudolife. Statistically, somewhere between a hundred hours and old age. We Erthumoi have partial recycling units in our suits which would take a thousand hours or so to run down if we lived on nothing else. You swimmers don't have any recycling, and need the fusers to concentrate oxygen for you, so there's a limit to the power we can commit to getting out of here."

	"We can't get the raft out. We know that already," Splasher pointed out, "and without the raft we can't carry the fermenters. If we try to build something smaller, it's an all-or-nothing project."

	Janice made a negative gesture, and the others paused to listen to her code.

	"One can go for help."

	Hugh pursed his lips thoughtfully.

	"I suppose so. Thrasher or Splasher couldn't swim all the way with supplies they can carry, though, and you or I would have to use some sort of jerried boat, either surface or sub. I suppose if we mounted several jets on something small enough it might make it. Would it be better to ride the surface and keep the oxygen problem down, or stay below and use diving juice? And if it doesn't work, what happens? One person at some unknown spot on or in the ocean, out of touch with both the raft here and the rest of the world, lost or out of power or both?"

	"The Job." The woman's code remark was terse but adequate. She paused a moment, then added, "Submerged. Navigation."

	"You mean it'll be easier to hold heading below storm level? I suppose that's right, though from what you and Thrasher say about the test dive it's pretty turbulent down below, too."

	"Low speed."

	Hugh was silent for some time. He knew his wife was slanting the arguments in favor of letting her make the trip. He'd have done the same if he'd been quick-witted enough, he realized; he couldn't blame her. He still didn't like the idea, though. He was not particularly protective as husbands went, but knew her tendency to overdemonstrate her already obvious competence, and even after four years of marriage couldn't help worrying just a little when they were apart. He curbed his thoughts firmly after a minute or so, since all three of the others were clearly waiting for him to speak.

	"All right. We'll have to do some designing and building, though, and we don't have much of a machine shop with us."

	"Basics," keyed Janice.

	"I know. The inclined plane. We have a knife apiece, and there are a lot of nuts and bolts in the thruster mounts. We'll have to scrounge material from what's around us, though, and make sure it's chemically stable."

	"You dry land and flying types have a violent idea of what makes the basic tool," Thrasher remarked. "Every one of you seems to regard the cutting edge as primary."

	"Well, what would you offer, and did you bring it along?" asked Hugh.

	"The rope, of course. Yes, we have several kilometers of high-tensile cord, though it's so thin we may have to pad it to keep it from cutting through other material. That's the real fundamental. Support for the helpless, towing burdens, nets and nooses for capturing food—the fiber started civilization, with glue and the lens next."

	Hugh was about to respond when Janice and Splasher interrupted together in almost identical phrases, though translator and coder didn't sound much alike. "Design now. Philosophy later." The males looked at each other, read what each was sure must be sympathy in the other's expression, and got back to the real subject.

	"How many thrusters should we risk? Will two be enough?"

	"I'd advise more," replied the Cephallonian. "There's a time question, and while Janice apparently can't travel very fast through turbulence, power is still relevant. It may be well to have drive force in reserve even if she doesn't want to use all of it."

	"All right. You two look over the local seaweed supply. I hope you know what's explosive by sight; with pieces the size we'll need, finding out the hard way is risky."

	"We know what furnishes safe cordage—which might be wise to use instead of our own reserves, when we can. Thicker samples of the same growths should make adequate frame members. We won't need too much if the rider is to be an Erthuma. Let's go collecting, Splasher."

	The seaweed that the swimmers selected was extremely tough and springy, but the knives of the human workers were able to deal with it. As much as possible was done aboard the raft, since a knife dropped over the abyss would be hard to retrieve. The Cephallonians might recover it before reaching their depth limit, but there were already enough problems. More of the high-tech cord was used than the swimmers had wanted, since the natural material they had hoped to employ was inconveniently thick when strong enough. In any case, the skeleton submarine produced in twenty hours or so of labor seemed sturdy enough. It was an open framework like those of the natives, partly to save time and material, partly to help the pilot's visibility. Four of the thruster-fuser units were lashed securely to it slightly ahead of what the group hoped would turn out to be its center of drag pressure. The hull diameter held opposite members of the thruster pairs nearly two meters apart; there had been some argument about making the craft so large, but the thought of having to lie prone for the whole trip was not merely unpleasant. Janice knew she would sometimes need to move around and her husband agreed that this was not just a whim.

	Lines of Cephallonian cord were gathered at a "panel" in front of the pilot station and led to the thrusters, where they were wrapped around the control potentiometers a dozen times to provide friction and let the pilot handle all four from one point.

	She would have to rely mostly on her own recycling equipment for food, and hope to reach the ring continent before it zeroed. Taking one of the fermenters along would have required an even larger craft, more thrusters, and divided attention for the pilot—selecting the right vegetation to feed the device was time-consuming.

	Hugh found no adequate excuse for changing the female pronoun of the pilot up to launch time, and unhappily watched his wife disappear into the depths. "If something goes wrong," he called after her, "just shut off the power and call for us. We put enough floats into that thing so the thrusters won't sink it!"

	"In the right places, I hope," muttered Splasher.

	Janice did call, very quickly. She was back in ten minutes, towed by the swimmers, and for once did not allow herself to be gagged by the code equipment.

	"It's lucky we spaced the drivers equally around this thing," she keyed, "and if we do get back, let's not report this whole episode in detail. I could only steer by changing thrust. The jets were far enough apart to have fair torque, but it was too awkward to manage for more than a few minutes. We'd better install some kind of rudders, lateral and vertical."

	Her husband raised his eyebrows. "A thought. It didn't occur to me, either, I admit."

	"I took for granted you planned to steer that way," said Splasher. "I thought of suggesting we mount them so they could be swiveled, but decided the control system would be too hard to rig and doubted that we could attach them firmly enough under such conditions. I agree about rudders."

	Making control surfaces was a fairly quick job: frames were easy, sheeting was cannibalized from the raft, and while the Cephallonians did not regard adhesive as quite so fundamental as rope, they did have plenty in their basic kits. More time was required to rig an additional system of control lines that Hugh could hope would neither tangle nor kink; and he was more uneasy than before when he saw the skeleton hull slide off once more into the weedy darkness, though his wife had spent some minutes in test maneuvers this time before actually starting.

	The moment she was out of sight he made his way to The Box. The artificial intelligence was still producing an almost real-time hologram of the surrounding ocean, a picture growing slowly in size and shrinking in scale as more and more sense was made of the chaotic ocean currents. The model depth, Hugh saw, was now nearly five kilometers at the center, the radius over forty. The image of Janice's craft showed clearly enough, and her husband cringed. Unlike The Box and the Cephallonians she had no sonar, and could not detect vertical currents until she was close enough to see the bits of luminous plankton whose motion would sometimes reveal them. After a few moments of watching, Hugh realized that she had accepted this; she wasn't trying to dodge but merely maintain depth, correcting the brief up or down accelerations as they came. Her attention must have been mostly on her inertial tracker, the man judged; he hoped she was sparing a little for really large explosive plants.

	He resisted the urge to call warnings as she nosed toward the bigger verticals. The Box could have produced sounds audible to her transducer easily enough, but she was already far enough away for signal delay to make warnings useless. She'd just have to take the jolts.

	Which meant she'd better not eat for—how long? He hadn't thought of that in detail. If Janice had, she hadn't mentioned it. And she had eaten before departure—stuffed herself as foil as she could to give her recycler as long a run as possible! And she was out there, soaked with diving fluid, with a stomach sensitive to motion, no real way to dodge those awful up-and-down currents, and no reflexes to keep vomit out of her trachea if she lost control!

	"Jan! Come back! You can't make it through those currents! We should have thought!"

	Dragging seconds passed before the code came back— long enough to make him wonder whether she had failed to hear or was actually ignoring him, and tempt him to call out again.

	"I did think. It's all right. I'm driving."

	He didn't get her point. "But Jan! How—?" he fell silent, not knowing what to say, but realizing his wife was not going to be argued out of her mission. Even before the partial sentence could have reached her, another message arrived. "Please don't worry, dear. I know what I'm doing."

	Hugh always wondered, but never asked, whether the attention she had given to the second message had anything to do with what followed. He couldn't see how, even after they finally figured out the cause, but there might have been something—

	Usually her code calls were extremely terse; this time she had used extra words, and therefore extra time. The coder must have distracted her, at least a little. He never asked, because he knew she'd never tell.

	The Box could spot currents, but there must have been something else. The submarine's image nosed into an unusually complex set of vertical patterns, and suddenly Hugh realized that it was no longer countering them but following, going down with the descending ones, rising with the ascending. For some reason Janice seemed no longer trying to maintain depth. Had she lost her tracker? Unlikely; it was part of her suit, and she was holding direction well enough.

	Explosive plant? The Box would have seen, heard, and presumably reported. An electrical encounter? Probable enough, but what could that have done? The submarine frame was of wood, which on Habranha did not necessarily or even probably mean a nonconductor, but her armor should be protection from any charge source they had seen or heard of so far.

	The Box had been making no speed readings on the image. Hugh had asked it to supply an enlarged view of the region around the craft but given no instructions about scale, so he could not tell how fast the machine was going, and there were of course limits to the resolving power of sonar that even The Box could not overcome. There was no way for it to show him the smaller plankton, and even large seaweed masses and animals were merely featureless dots in the hologram.

	But dots motionless with respect to each other were probably seaweed, and they were drifting past Janice's vessel surprisingly quickly ...

	"Box! Doppler the sub!"

	Since The Box had merely been correcting for doppler without displaying it, the visible response was immediate.

	"She shouldn't be going that fast! All four thrusters must be wide open! Jan! Jan! What's wrong? Are you all right?"

	There was no immediate answer, but Hugh was not completely out of his mind. He could still allow for message delay.

	Code finally sounded from The Box's relay unit.

	"Thrust control. Shaking loose. May abandon. Watch."

	With clenched fists and bitten lips, Hugh watched. He called the Cephallonians, and The Box without instructions set up a larger display in their tank so that they could see as well, but no more was said for the moment. Instructions were useless; Janice would know what she was doing, what she had to do, and when it had to be done seconds before any of the others could tell. It would be nice to know what had gone wrong with the drivers, but asking her now would be somewhere between futile and dangerous.

	They watched while the eight-meter-long framework drove into an upwelling current of nearly four meters a second at roughly three times that speed. The display showed a small object separate from the submarine and sink for twelve or fifteen meters, halt with a jerk with respect to the craft and remain matched to its vertical speed. Hugh sighed in relief, but ground out some words between his teeth.

	"For sense's sake, dear idiot, positive buoyancy!"

	Thrasher was almost as upset, but spoke more sensibly. "I don't think that's Jan, Hugh. More likely one of the thrusters, judging by weight, held by part of the original lashing somewhere ahead of the center of buoyancy. Look at the sub!"

	The framework was nosing downward, and starting to move in the same direction.

	"Cut it loose, Jan!" cried one of the Cephallonians. "You'll never get the bow up with that thing hanging from it!"

	Even Hugh realized that his wife's weight could never have produced that much effect, tricky as the sub's balance had proved to be and regardless of any buoyancy she might have adjusted in her suit, and decided the swimmers were probably right. This did little to make him feel better, however.

	The Cephallonians were loading oxygen tanks; they hardly ever removed their suits—the ammonia of Habranha's ocean irritated their skins. Even here at the warm pole, where the stuff was least soluble and occurred mostly in the air, forcing their Erthumoi companions to wear breathing masks even out of the water, the swimmers needed protection. Near the Solid Ocean, as the natives called the darkside glacier, where Erthumoi could breathe unprotected for minutes with little discomfort if they were careful about hyperventilation on the extra oxygen, Cephallonians found the water much worse. Now, therefore, they were ready for the rescue in moments. There was no need for talk; they knew The Box would guide them and provide information updates, and they didn't need requests or instructions from Hugh. They plunged into the waves from the open stern of their tank, and the Erthuma watched their departing images in The Box's main display.

	If that dangling object were a loose thruster and not Janice herself, why didn't she cut it loose? With the sub now traveling downward, why didn't she cut herself loose if that were her own image or get out if it weren't? Clearly the craft was out of control. Granted it represented a lot of work and, for the group, some irreplaceable equipment, but Janice wasn't stupid. As long as she were conscious— if she were—

	Hugh Cedar clenched his fists and watched the special display even more closely, wondering whether the swimmers would reach the foundering sub before it got below The Box's range of clear perception. He cursed luridly every few seconds as the artificial mind changed its electronic opinion and modified shape or position of some part of the picture to fit new data. He could have argued with it, since the Cephallonians were too far away to be bothered by his treating a machine as a fellow being, but no number of words would have been any improvement in detail on the image, and would certainly have been far slower.

	Why was she staying with the sub? Had something knocked her out? Had motion sickness overcome her, and parts of that huge last meal blocked her air passage? Was she still inside the vessel, or was that, in spite of logic, her armor hanging meters below it? He kept reminding himself firmly that she should float; even if the suit leaked diving fluid, any freed volume would be replaced from emergency oxygen tanks and the overall density reduced. The dangling blob must be a loose thruster, as Thrasher had insisted.

	But why wasn't she doing something about it? And when were those jellyfish going to get to her? He spoke to The Box for the first time in-minutes.

	"How far do they have to go, and what's the closing rate?"

	"Six point seven one kilometers equivalent distance. I am guiding them on a path which allows for all current deflections. They should reach the sub in just over eight minutes, which I assume is what you really wanted to know. The meeting should occur well above the depth limit of the Cephallonians, so you need not worry."

	"I hadn't thought of worrying about that. Thanks. Just how sure are you whether that hanging thing is a thruster, as Thrasher said, or Jan herself?"

	"It is much too dense to be human armor, even occupied. That interpretation had not occurred to me. If I had known you were concerned—"

	"Then she's still inside the sub?"

	"I would certainly have observed her separation."

	"Then what's the silly darling doing? Why is she heading down? I know she can take any pressure this world can give, loaded up with diving fluid, but a few more kilometers and she'll be out of reach of any possible help!"

	"Are you being rhetorical, or do you want me to ask her?"

	Hugh hesitated only an instant. "Rhetorical, I guess. She could be busy enough for interruption to be dangerous. She must know we're watching and worrying, and will report when she can—if she can ..." His voice trailed off.

	"You are quite sure?"

	"No, not quite, dammit." Hugh pursed his lips grimly. "But with Thrasher and Splasher on the way, that's how I'm going to have to play it. Give me all the resolution you can in your images, and all the sense you can make out of any conversation you hear."

	"Of course."

	"And if I jump off the raft and start swimming toward them, tell me I'm an idiot."

	"Why? You will know it already. I will merely direct you back here, as soon as you are far enough away to need it."

	"Then I'll go the other way."

	"I know."

	That silenced Hugh, whose attention had never really wandered from the display. The swimmers were closing in on their target, now, and visible in the special display. The Box had deleted the vertical current symbols to clear the view for the Erthuma, but there was still a good deal of ambiguity that it kept resolving now one way and now another as the weight of incoming evidence, in the form of sound waves of varying frequency and phase, kept shifting.

	The electronic intelligence seemed sure that the dangling object was a driver rather than a human form; it had said so. Hugh's mind recognized the weight of the evidence, but even though he was adult and a scientist his mind wasn't in full control. Not until he saw the two swimmers close in on the sub without paying attention to what was hanging from it did he relax slightly. At that range the Cephallonians could easily tell either by sight or sonar what the suspended object was, and if they were concentrating on the craft—

	Abruptly the man felt as though his own breathing system were full of diving fluid. Both swimmers suddenly swerved downward toward the suspended object, and their blurred images merged with it and each other. For long, long seconds no change could be seen; then both The Box and through it the Erthuma could tell that the Cephallonians were rising and the submarine once more nosing upward toward a horizontal attitude.

	"They've asked for guidance back here," the artificial intelligence reported in its usual calm tone. "What happened?"

	"Janice doesn't know. Something caused all four thrusters to build up to full power almost simultaneously, and the bottom one tore free from most of its lashings. Its weight and the unbalanced push of the top one before she could shut it down caused the sub to nose downward. The hanging thruster had broken its control cable before she could shut it off too, so it was still operating, also pointing down."

	"Why didn't she cut it loose?"

	"I will ask. I would guess she didn't want to lose the unit, and felt she could pull it back within reach by the lines still holding it. She was in no obvious danger; she is equipped to survive at the full depth of this ocean."

	"Except that the power units were not responding to control."

	"She did manage to shut the three off. No doubt, though, that is why the Cephallonians think she should return. There was argument, though I could not hear all of it."

	"At least Jan's all right."

	"It seems so. I expect her main trouble will be annoyance, if she has not been able to decide why the thrust units went out of control."

	"You have no idea?"

	"None. They worked perfectly driving the raft, and I can see no reason why a change in mount should make a difference. Intake and discharge areas were clear on the submarine, if anything clearer than on the raft. The thrusters and fusers are complete units. Nothing like intake filters, ion dischargers, or electrolyzers are separate, so nothing could have been omitted inadvertently during transfer.

	"Since none of us is a mechanic, that's just as well. I guess you're right, then. If Jan hasn't figured it out by then, she'll be highly incensed when she gets here. D'you mind if I arrange for her to take it out on you?"

	"I don't mind, but doubt that you'll fool her that easily."

	"So do I," Hugh answered gloomily.

	But if Janice were angry, she hid it well. She had no explanation for the misbehavior of the drivers, though she felt normal scientific curiosity about the matter. She would also have liked on purely practical grounds to be able to use them in saving the lives of the group. However, she was a rational person, and having accepted that they were not trustworthy she had already dismissed them from consideration. She was still as concerned as the rest over what should be done next, and her remarks focused on this.

	They were all feeling increasingly that while time was not exactly standing over them with a poised axe, it was in the front row of seats with a guess-where-I-put-my-money smile on its face.

	"I hate to say it," Janice keyed as she reboarded the raft, "but I'm afraid the juice had better go back in the tank. No more diving, little more project. We need to get our present information home, not to mention ourselves. Then we can carry on with better-planned equipment."

	Her husband certainly did not object, and they set to work. Getting the last of the chemical out of her system took time and care, and several hours of therapy were needed to restore Janice's damped-out reflexes. Both of them were now experienced at this, however, and the Cephallonians could continue some project work in the meantime.

	Janice marked the completion of the therapy by a couple of hours of acute seasickness; the nausea she had been firmly holding back for over two weeks ran wild, probably with some aid from her imagination. Then, with firsthand assurance that her antichoking reflexes were working as they should, both Erthumoi were able to turn their minds back to the survival problem.

	"Box, why couldn't Thrasher or Splasher swim back to the continent if we made a small raft for one of their fermenters? Couldn't they maintain an average speed higher than the incoming current?" Janice asked, rejoicing in her voice. This had been suggested before, but not with the tow detail.

	"Not even with the most efficiently streamlined raft we could make," replied The Box unequivocally. "Food would not be the limit. They would run out of oxygen much more quickly. The air here is less breathable for them than for Erthumoi, power is needed to separate oxygen for their suits, and you have said that we can't rely on the power units."

	"We have been relying on them for that," Hugh pointed out.

	"Only here on the raft. We don't know why they didn't work away from the raft," his wife insisted. "The Cephs couldn't possibly carry tanks enough for the trip even if we had enough or could make them. They'd need separating equipment and pumps—power. We can't take that chance. They were able to pull me out of trouble when it happened only a few kilos away, but who rescues one of them a quarter of the way to The Iris?"

	"We expect to take chances." Thrasher considered his professional conscience as good as that of Janice.

	"Reasonable chances only. If the rescue effort fails, we all die, the rescuer in some possibly interesting fashion and the rest starving while we wait and wonder. We already know the fusers are unreliable in travel, even if we don't know why. If someone does figure that out, it's a new game; but until that happens we count them out." Janice was firm, and Thrasher, who had not been really enthusiastic about towing a raft of equipment and food, said no more. His wife, however, cut in rather pointedly.

	"Where is all this leading? Someone has to take a chance, and no one has suggested any way of getting out, except swimming, which doesn't use power units. I assume you're not suggesting that you Erthumoi swim for it—or row. You'd make no headway against even the current, much less the wind, even if we could make you a boat."

	"We could manage a boat all right," Janice said thoughtfully, "After all, we did improvise the sub, and there's a lot of fabric still on the raft. But you're probably right about the wind."

	"In principle," Hugh said thoughtfully, "I suppose one could use wind power to drive us against the current. We could have some sort of wind turbine which drove another rotor under the surface. The water has more inertia—how about it, Box?"

	"Quite possible in principle. Very doubtful as a practical project with the material and tools and, I must regretfully point out, the skills available here."

	Janice raised her eyebrows. "Come on, darling. In my education they stressed the difference between comprehension and craftsmanship."

	"Hmph. In mine they called 'em mentality and manipulation, and said any time we saw a gap between 'em we should try to close it."

	"The translators are having trouble," Thrasher cut in.

	"Sorry," answered Janice, "we went a bit astray. The question is still how to get someone or something to carry news of our troubles to where it has a reasonable chance of being found. You folks need food and oxygen in huge amounts, we Erthumoi can't travel far or fast under our own power, and The Box—hmmm. What can't it do?"

	"It can't handle emergencies," the artificial intelligence pointed out, using third person to keep the Cephallonians a little happier. "It's the gap Janice mentioned. It can do practically nothing. You could have built connections which would have let it run your submarine, for example, but it could only have called for help if anything went wrong. No real imagination, only preplanned effectors. If you are proposing that it guide a boat back to Iris, the advice is no. The guidance is easy to find, and there would be no food or oxygen problem, but you would have to use a fuser to power the boat; and we are back to our ignorance of just what went wrong."

	"Then we're stuck, it seems to me," said Hugh. "We can't use power. It takes power to buck current below the surface. It takes power to buck wind and current at the surface. It takes power to buck wind above the surface— for that matter it takes power to fly at all. And we can't use—"

	"Does it?" Janice perked up suddenly.

	"Does it what?" both Cephallonians asked simultaneously. Hugh knew his wife well enough to resolve the ambiguity.

	"Yes. It takes power to fly," he said firmly.

	"No. There are plenty of vertical currents in the air as well as the water. A sailplane can use them—"

	"If the pilot can find them. And are you suggesting we can build a sailplane? I know they're simple basically, and we've both flown them, but we've never made one— remember your remark about craftsmanship a minute ago. And how would you propose to launch it if we did make it?"

	"Kite style, with the Cephallonians pulling. There's plenty of wind, reason knows." Janice was wearing a smile that Hugh recognized even through her face protection, but he wasn't quite ready to give up yet.

	"And you think you can fly one here? Where winged natives themselves don't dare come? Where it isn't just a matter of looking for another thermal to head for after you reach the top of the first? You know as well as I that Habranha should have been called Chaos—it just looks like an eyeball. There are no simple currents here, air or water!

	"Box, will you please straighten out this crazy woman? Could the Cephallonians pull a sailplane fast enough to get it off the water—wait, dear, I'm not done—if it were designed to glide faster than the winds it would have to buck? In this gravity, what sort of shape would it have— what sort of wing loading?"

	"Wait, Box!" insisted Janice. "How high would we have to fly to avoid the really strong wind into the evaporation zone? Would we need oxygen? And for how long? Remember the winds aloft carry clouds back toward Darkside."

	"True," replied the artificial intelligence. "The scale height on Habranha, particularly in the Cataract area, is large, though there are no exact figures. In view of the high surface oxygen partial pressure, you can probably breathe unaided at heights well above seven kilometers, and at such altitudes the main circulation is toward Dark-side. You need not make a high-speed craft; low wing loading, such as you would use on a planet of Erthuma-comfortable gravity, will be adequate—indeed, highly advisable, since there is no reliable information on how far you would have to travel between updrafts. Launch in the way you suggest should be quite possible."

	"It's still silly!" Hugh was almost snarling. "We've flown in calm atmospheres, with nice, steady thermals a few kilometers apart, marked with cumulus clouds at the top. You know it's not like that here! You—"

	"What else can you think of?"

	The only answer Hugh could have given to this grossly unfair question would have been to point out its unfairness. He didn't bother; Janice knew that as well as he did. He was silent.

	The woman refrained from triumphant remarks, which would have been even more unfair, and even blanked her facial expression now. She did love her Hugh. She also knew that he might be right; not even The Box could have considered everything. She was, however, a determined person, and greatly preferred doing something even when not sure that it was right. After all, as any scientist knew, there was never any way to be completely certain. Not objectively, and faith was inappropriate to the present problem.

	The submarine's frame served as basis for the glider. To the long hull, now a fuselage, were added wings of twelve-meter span and one-meter chord at the root, far more area than was really needed in Habranha's gravity. They were designed carefully with the aid of The Box and assembled even more meticulously. It was embarrassing to Erthuma and Cephallonian alike to find that they needed to make their own measuring devices before doing any cutting; construction of this sort had not been planned for the study. Work was not really delayed by the resulting philosophical debate about fundamental equipment, but the debate served as background.

	The hull had to be covered carefully with sheeting from the raft, and only the upper surfaces of the wings could be treated similarly before supplies ran short. Hugh would have liked well-shaped airfoils, but a fuselage that would float and not collect weed on its frame members while being launched, as the submarine had done even on its brief trip, seemed still more necessary. Also, there was no easy way to find the center of gravity unless the object were floating, though this could of course be shifted somewhat in flight by having the crew shift. The cockpit was open, longer than necessary merely to contain the Erthumoi; the crude seats were easily movable to permit this.

	Seats, plural. Hugh was for once firm. His wife was not going alone this time. She made little argument and the Cephallonians none. It made no difference to the swimmers, and she was glad enough to have him along.

	The other possibility, that he might make the flight without her, never crossed her mind, and if he thought of it he had the sense to keep quiet.

	The Cephallonians were ready to make another rescue trip themselves, but courteously said nothing about it. They would have more difficulty this time, of course, since The Box had no sense of what went on above the ocean surface and could present no image of the atmosphere. If the glider had trouble, no one below would know until it reached the ocean, and then only if the accident occurred within the radius of the current sea image. It was quite possible, everyone including The Box realized, that even within that range a splash might be misinterpreted and go unnoticed; once in the water, the crew would have to use their transducers and signal as loudly as possible for help.

	Splasher remarked to her husband, translator off, that she didn't think the Erthumoi would get half a kilometer vertically or horizontally; if the Habras themselves didn't fly in this region it seemed pretty silly for walkers to try it. Thrasher gave the equivalent of a nod.

	Hugh had not repeated his essentially identical opinion since the initial argument, but it remained unchanged. He made sure that their environment suits were still adjusted for positive buoyancy, and was somewhat relieved when he saw his wife unobtrusively making the same check. This might, of course, have been mere routine, not pessimism or even realism, but at least it was being done.

	They checked their suit filters with even greater care, and loaded a few oxygen tanks for possible need—only a few, since they did not expect the glider to be able to take much weight, and the swimmers might have a hard time with the launch no matter how light the machine was kept.

	The real uncertainty was in wing symmetry. Even a slight warp, too minute to spot by eye alone, would mean a built-in tendency to bank and turn, and eyes were all they had—no precision assembly jigs or anything else "precision." With someone at the controls, of course, such a warp could be countered, but that would mean a constantly alert pilot. Hugh had planned and started to build the wings so that they could be rotated around a lateral axis in flight, the axis represented by a single main spar, before his wife convinced him that any significant motion of that sort would mean gross overcontrolling. As an experienced recreation sailplane pilot himself he had known this perfectly well but had been highly pessimistic about their ability to build a really symmetrical pair of wings. He still was, and was not looking forward to the launch with any great confidence. Naturally, he wanted to be at the controls himself during the process. For similar reasons, so did Janice.

	To minimize any temporary warping the wings were rigged with cord provided by the Cephallonians, though as little of this was used as possible. Even if weed could be picked up only during launch, any would be too much; there was no way such a load could possibly turn out to be balanced, either as weight or drag.

	There was little doubt by the time it was assembled that the glider would fly kitewise, as long as its launching lines were held from below and someone was controlling its roll; there was always enough wind for that. The question was what would happen when those lines were cast off. It would then be necessary for the Erthumoi to find, or better to have found already, a wind with at least some upward component within gliding distance. There were plenty of spouts where ammonia was leaving the ocean violently, and these should have velocity enough to offset their lower density and lift; but whether the glider would hold together inside their violent structures was decidedly doubtful. On more Erthuma-normal worlds sailplane pilots stayed out of thermals that were growing thunderheads at the top; on this part of Habranha one could not see high enough to tell when this was the case. Free ammonia met water vapor, or much more rarely even hydrogen cyanide, in concentrations high enough to form clouds sometimes quite close to the ocean surface, though the adiabatic lapse rate was small. Thunder was nearly constant in The Cataract, the flicker of lightning sometimes detectable even in the constant daylight, but their sources could seldom be located. It was obvious only that they were high. The thunderheads were out of sight.

	Janice was in the cockpit, and the Cephallonians a hundred meters away holding what all hoped would serve as launching lines. Hugh was casting off the numerous cords they had found necessary to keep the glider from blowing away as it neared completion. He trusted his wife to hold it firmly down until he could get on board, but made a point of leaving until last the tiedowns at the forward end—after all, neither of them knew just how effective the control surfaces would be in air, though they had worked well enough when the craft was a submarine. The specific question was whether they could hold the tail high enough to keep the wings from lifting at any time on a pitching deck. Several times during the unmooring the man leaped gliderward as the raft tilted the nose up, wind caught under the wings, and for a moment the fuselage rose and strained upward against the remaining ropes. It promised well for the flight, but made the casting off a nervous procedure.

	"Box, have them take up the slack in the launch lines," Hugh called as he approached the last two moorings. This order obeyed, he reached for the nearer of the two; then an idea struck him, and he went back to the cockpit, knotted another cord to an exposed longeron by his own seat, and with the other end of this clipped to his suit went forward again. The moorings clear, he ran and handover-handed back to his cockpit, wondering simultaneously whether his wife could hold the craft down for five seconds and why they hadn't thought to improvise some means of releasing all the moorings at once from on board. He reached his goal without being lifted off the deck, slid over the side as quickly as his suit allowed without risking the fuselage fabric, settled onto his lurching seat, and tied the multiply-braided cord intended for a safety belt across his legs. Looking up from that precaution, he saw that they were already eight or ten meters above the raft— straight above; the swimmers hadn't yet started to pull.

	Whether they were flying, as opposed to blowing around, was debatable. Janice was certainly using her controls. These consisted of a horizontal foot bar on a vertical axis with lines from its ends directing the rudder, and two vertical rods: one for ailerons manipulated by her left hand, and one for vertical control at her right. Each set of lines had another bar within Hugh's reach as he sat behind his wife, though he had to lean forward rather awkwardly for the aileron one. This was from his seat's present position; it might turn out, they knew, that his would have to be moved so far back or hers so far forward to balance the glider properly that only one could reach controls at all.

	The craft was far from steady so far, dipping, soaring, and yawing. The wind was doing all the lifting; the swimmers were holding position a hundred meters from the raft, and the Erthumoi were oscillating above it. Janice was still overcontrolling but learning quickly, and their crewed kite began to settle into a steadier pattern—not perfectly motionless, of course, in Habranha's chaotic air currents, but something far more comfortable than it had been at the start. Hugh wondered briefly how his wife's motion-sensitive stomach had been able to take the first few minutes, and then recalled what a difference it made when the owner of the stomach was doing the piloting. She had been right to insist.

	She had almost completely stopped the roll and yaw wandering now, and was managing, on the average, a gentle climb. The tow lines were taking on a remarkably steep slant, and Hugh almost automatically began estimating the lift and drag vectors involved. The weight was small enough, but it wasn't zero even on Habranha. Was there an updraft anywhere near that could support them?

	A spout showed half a kilometer to the left, reaching up into the haze beyond human vision; another was behind them, presumably being carried away by the wind now holding up the glider. If they cast loose from the Cephallonians, what would be their glide angle? Could he compute it from the present slant of the rope? Not without knowing the wind speed, of course.

	Their trackers would let them calculate the last only after they were free. Then they could get glide angle from the recent rope slant, assuming wind was reasonably constant, which was asking a lot. Then they would know if they could get close enough to the spout to use its vertical air currents. If they couldn't—if the glide were too steep— well, they could land on the sea and the Cephallonians could tow them back for another try.

	Or they could wait as they were until a spout came so close that there would be no doubt about their reaching it.

	Or maybe they shouldn't use a spout. A whirlpool should have a less violent lifter above it. Less likely to tear wings off. The endlessly varying howl of The Cataract's wind didn't completely drown out the occasional mutter of thunder that reminded Hugh of what real thermals could do to aircraft—even professionally built ones. Neither he nor his wife had any illusions about the rugged-ness of the gimcrack device they were riding.

	Hugh saw a whirlpool a few hundred meters to their right, and pointed. Janice nodded silently. The launch cables, unlike the tie-downs, had been arranged to be released from the cockpit; she dropped them at once and swung right in a slightly overcontrolled but fairly graceful turn. She was trying to find the narrow line between maximum glide range and stall attitude as she headed for the possible source of lift. They had no airspeed instrument; their inertial trackers were useless for any such problem, of course, without independent wind information. Almost useless; they did show local vertical, since Habranha's radius, rotation, and even its orbital parameters had been set into them.

	The glider recovered easily from stalls, it turned out, and the pilot lost control only twice. Fortunately, wings stalled before control surfaces. This was rather surprising, considering the history of the latter as hydrofoils, but neither of the crew thought of that.

	They still had reserve altitude when they felt an upward surge. Janice glanced over her shoulder, and each could see a grin of triumph through the partner's face protector. The woman concentrated on a gentle turn that kept them in the updraft, using her trackers after the raft faded from view in haze below them. At four kilometers' altitude they ceased to climb; the current was just able to support them. She straightened out in the planned direction—headings were not quite all equivalent. All points on The Iris's near edge were about equidistant from the substellar pole, but the raft was much closer to one side of The Cataract than the other. There was, however, no way to tell where another updraft might be found, and this was the more immediate problem. Janice was pretty certain now of the ideal glide attitude, and maintained it with the aid of the vertical-component tracker since no horizon was visible.

	The other component readings suggested for some time that wind was helping them on their way, as The Box had predicted. Below about two and a half kilometers added turbulence heralded the end of this status and their true descent angle steepened, though the glider's ideal attitude did not of course change. Just below one kilometer the ocean surface became visible once more, and both Erthumoi began to search it earnestly for signs of another rising current.

	Several spouts showed up almost at once, clustered rather closely together for reasons known only to chaos; no others could be seen within the ten- or fifteen-kilometer range that the slight haze permitted to Erthumoi vision.

	Whirlpools would be smaller and harder to see, of course. The flyers had the obvious choice of a straight-line glide that would cover more ocean, get them farther on their way, and in theory give them a better chance of finding whatever lifters there might be, or circling to remain within gliding distance of the spouts in case no whirlpools could be found and the more dangerous alternative had to be used. Hugh said nothing when his wife banked the glider into a gentle turn that kept them circling the spouts. He would have made the same choice. They seemed risky, but at least they were definitely there.

	Two-hundred meters above the raging surface Janice glanced back at her husband once more. He shrugged. She nodded, and started another slow turn in toward the nearest column of ammonia-rich spray.

	The glider was already shuddering in turbulence, and maintaining a steady descent was not really possible. She did not, of course, head straight into the misty pillar but a few dozen meters to its left. They should still be nearly a hundred meters above the waves when they came level with it, and ought to be feeling lift before then.

	They did, but under the right wing only. The glider went into a nearly vertical bank to the left and started a steep diving turn in that direction. Hugh's training normally kept him from being a control-grabber, but this time he helped; between them they leveled out at thirty or forty meters. The man released his bars with a major effort of self-control, and Janice promptly and deliberately nosed down again to gain speed and banked back toward the spout—straight toward it. This time the nose felt the lift first, but she forced it down firmly. Hugh nodded silently, not looking at the chop ten meters below. Only when Janice felt strong general lift did she turn once more to bring them side-on to the spout.

	Now the difference between the two sides was not so great and she was able to maintain control, and even to hold the inner wing—the left one this time—down so they remained in a slow turn and stayed inside the lift region. They were climbing again, far faster than before; Hugh felt uneasy as he saw the wings bending visibly.

	Not bending, flapping. A little yield was normal for any structural material and the woody stems they had used for the frame were extremely springy, but this shouldn't be happening. A steady updraft might have bent them during the initial acceleration, but once they were lifting steadily—

	They weren't lifting steadily, of course. Habranha's chaos was manifesting itself again. The glider was jerking and twisting, pitching and banking and yawing in gaseous eddies quite undetectable until one was in them and, Hugh guessed, quite beyond the power of even The Box to resolve into a predictable pattern had it been with them.

	"Cut out of this!" he cried to Janice.

	"We need more altitude. We have less than a kilo so far. We've got to get higher!"

	"We need wings and tail more. We've got enough to give us some gliding range. We can look for a safer updraft."

	"But at this height the main wind is still toward The Cataract."

	"We can live with that. We were expecting lots of climb-and-glide cycles before we got anywhere near where we wanted."

	"But that first one—"

	"Don't let one piece of luck spoil you. Get out while we have wings!" Tense as he was, Hugh made no attempt to seize the controls; he was a recreational flyer, not a professional, but too good a pilot for that. A vehicle—any vehicle, land, ocean, air, or space—must be controlled either by a single entity or by a completely cooperative and informed team.

	If there are two or more experts aboard, the one actually taking a turn at the controls is responsible.

	If there are no experts aboard, of course—

	Hugh controlled himself just the same.

	Whether Janice decided to follow her husband's half-panicky advice or was simply overpowered by turbulence that might just as easily have driven them more deeply into the spout she never said, and Hugh didn't ask, but things gradually quieted down. The bouncing grew less violent, and it became possible to maintain something like flight attitude and even a vague direction with the aid of the trackers. There was still no horizon; visibility had become much worse and the usual thunder louder and more frequent, though lightning even now could never be seen as more than a sourceless flicker in the haze. The wings and tail ceased to flutter seriously, as did Hugh's nerves.

	Janice, however, was bothered. "We're not climbing."

	Her husband checked his own tracker. "Sure we are. A meter every fifteen seconds or so."

	"That's nothing. We got over three meters a second out of that first lifter and something like five times that from the spout while we were in it."

	"Be calm. We're going up, and heading the right way—you're not circling."

	"That's the trouble. This updraft has to stop soon, or rather we're bound to fly out of it, and I don't know which way to turn to get back in."

	"Back the way we came, of course."

	"Not if I can help it. The idea is to get to The Iris where we can find someone to help Thrasher and Splasher."

	"Come on." Hugh let his impatience show. "You're letting yourself get spoiled again. Even I don't expect to make it in one straight leg. Gliders don't work that way, and you know it as well as I do."

	"I know. But do you really want to fly back into that spout? We won't see it coming, you know—not up here."

	"We can stand it for a few seconds. You got out before. You'd better turn back—we're descending now, and you were right about our needing more height."

	Janice shrugged, nodded, and put the glider into a shallow right turn. Thirty seconds after completing the half circle their descent stopped. "Not too wild up here," she remarked. "I'll hold for a while, but do a ninety to one side and see if we can climb with ten-minute back-and-forth legs before we get back to where the spout was. You have its tracker readings?"

	"Burned on my cortex," Hugh assured her. "I'll give—oh, three kilos' warning? Or would you feel happier with five?"

	"One," his wife said firmly. "We want lift. Remember?"

	"All right." Hugh tried to conceal his uneasiness and might have succeeded; at least, Janice said nothing more.

	The spout, however, did a much better job of concealing the fact that it was not a simple vertical column. That, at least, was what the Erthumoi decided later. They met the wild turbulence long before Hugh's warning was due; Janice instantly started a steep left turn and before completing the intended ninety degrees was into chaos far worse than before.

	She tried to reverse the turn, but found her efforts fully occupied simply making the glider fly rather than blow away. Holding her eye on the tracking indicators, she did her best to keep the machine in a slight right bank and with the nose down in what she had decided was best-range glide attitude—this should keep airspeed, and therefore stresses, at a minimum. It did not prevent violent jolts as they struck eddy after eddy with no obvious regularity. Chaos continued to reign, thunder was louder, and twice in the next few minutes lightning flashes were actually visible. They were rising, on the average but not at all regularly. Hugh tried not to look at the slender wings, which were whipping madly again, but to keep his eyes on his trackers or his wife. He felt himself jerked against his safety cord with each flap of the wings, and began to worry about that. Should he hold on to the frame, or Janice? He didn't want to distract her, useless as her flying efforts might be, but if her safety line went—

	He reached around her, as unobtrusively as he could, using the piece of cord he had employed on himself just before the launch, and secured her suit to the seat with part of it. Then he cut off the unused couple of meters and employed it to do the same for his own. The turbulence seemed to be easing—but how often could they repeat this sort of thing, and for how long could they keep it up? How long would it take them to get out of The Cataract? One more climb and glide, or a dozen? The area of high evaporation was irregular in shape, as he remembered—he had seen it from space, of course, when they were first approaching the planet that all Erthumoi nicknamed Eyeball at first sight, and the irregularity would be in time as well. For that matter, the shortest direction out might not be the same any more; his arrival had been months ago, and The Cataract probably changed its shape significantly in hours. They had known when they started the flight that the raft was not exactly under the sun, and had headed away from that pole and tried to keep the average heading unchanged. The trackers indicated that they had been only partly successful. They could still only do their best.

	Just fly. Hold your heading on the long glides. Get all the altitude you can, glide as far as you can, find a lifter if possible, and repeat.

	An abrupt upward jolt, more violent than anything they had felt so far, brought Hugh's mind back to real time. He looked at the wings with a sinking sensation that had nothing to do with real motion as they bowed upward for more than two meters at the tips, wrinkling the covering fabric—briefly, the man felt thankful they had not covered the bottom; then, still intact, they whipped back to and past their normal shape, prolonging for a moment the upward ride of the fuselage.

	And at the top of that ride Janice, seat and all, left the glider. For a moment she hung above it and Hugh reached for her, but he was not quick enough and would probably not have been strong enough. With the aircraft's center of gravity shifting suddenly backward it pitched upward and its wings took a deeper bite of the air. This brought the fuselage up toward the errant pilot and for a moment she seemed about to return to her proper place; but drag had increased even more than lift. She struck the body well ahead of the cockpit, slid off after a futile attempt to reach through the polymer sheeting and grasp a longeron, and fell—not rapidly, on Habranha, but she fell. Her right hand caught a wing rigging line, and the glider went into a vertical bank. Before Hugh could react, Janice deliberately let go.

	The man slid his seat forward without hesitation; like his wife, he had spent much time thinking about possible emergency actions with their untested craft, and many of these had involved balance. He seized Janice's controls, no longer able to reach his own, and without the slightest concern for air speed or structural strength brought the nose down as far as it would go.

	This was not a vertical dive or anything like it, and he had to bank into a tight spiral to bring his wife back into view from under the nose. He was losing altitude, of course, but not nearly as fast as she was, since they were both still in the updraft but the glider was far more affected by it.

	For a desperate, unreasoning moment Hugh wondered whether it would do any good to try to hack the wings off with his knife to make his fall faster. Memory of the toughness of the woodlike material they had used for framework, a toughness so well displayed by the wings in the last few minutes, made him decide against it even before he thought of what the fall would be like after getting one wing off but before disposing of the other. After a fleeting and futile thought about the convenience of explosive bolts for quick disassembly, he brought his mind firmly back to reality.

	He would have to keep her in sight, obviously. There was sunlight enough, hazy as the sky was; it was little over a kilometer to the surface; Jan's suit would certainly float; it was simply a question of not losing track of her, and landing—no, "ditching" was the word, wasn't it?— as close to her as possible.

	And then they could call the Cephallonians. The one glide they had made could not have taken them out of The Box's model range, surely. Of course, part of it had been made with a tail wind of unknown speed—don't be silly, Cedar. You don't need dead reckoning; the trackers will tell you. But you can't look at them just now; you can't take your eyes off Janice. She's starting to blend in a little too well with the haze. But you were reading them often enough a few minutes ago; what did they say?

	Hugh couldn't remember. Too much else had happened in recent moments to monopolize his attention. He'd have to worry about calling the swimmers after he'd landed and picked up his wife—where was she? He squinted, and shook his head. There were several specks in his field of vision, most of them moving erratically, and he couldn't be sure which if any was Janice's suit. It had blended in with the background, as it had been threatening to do for seconds-He couldn't go straight down. The glider wouldn't enter a vertical dive. He tried once more, with his own body as far forward as he could get it, but the broad wings had too much drag and were too far above the center of gravity, and the elevators didn't have enough area.

	But there was another way. He had heard of it, though he had never flown anything unstable enough to experience it. He brought the nose up, and for the first time hoped that the glider's long wings were not absolutely warp free.

	They weren't. The right one stalled out first, and a moment later the glider was in an almost flat spin as nearly straight downward as the local winds allowed. Actually, it was hard to tell by eye that he was descending at all. The spin was slow, thanks to the lightness and span of the aircraft, but it was still hard to fix the eye on any reference point in the haze. Certainly not on his wife.

	The tracker insisted that he was going down, however, though probably a lot more slowly than she. He could only guess at the terminal velocity of a human body in Habranhan gravity and air, but the guess was many times higher than the tracker's quarter-meter-per-second reading. This did increase somewhat during the next minute; either the lifting current was not vertical, as he had already guessed, and the fall was taking him out of it, or the turbulence was doing its usual statistical job of working the glider into a quieter area. He hoped it was the former, which would give him a much better chance of hitting the ocean somewhere near Janice.

	The water was not encouraging when it became visible. It still showed the mad choppiness of The Cataract area. Spotting a nearly submerged human form in the waves, spray, foam, and seaweed would be hard enough on the way down, and hopeless when being tossed around among them himself. Janice could be floating fifty meters away and easily be missed. Even if he did see her, moving the glider over for a rescue would be impractical. There was nothing to serve as a paddle, she would probably be unable to hear his calls over the roar of wind and wave and thunder, the fuselage floated high at the mercy of the wind, and if he left the craft to swim over to her it would probably be impossible to get back. No, he could use a safety line, since there was plenty of rope; but he would still have to see her first.

	He certainly failed to do that before settling with surprising gentleness onto the waves.

	The good part was the tracker claim that he was only about twenty-two kilometers from the raft. The single real glide they had made had been good, but not outstanding; it would have taken them a long, long time to reach The Iris that way.

	The Box should be able to hear a call for help. Maybe Janice, who must have hit the water first, had already reported and the Cephallonians were now en route.

	Even if she had he should also check in, of course. He unclipped the transducer from his suit, reached over the side to hold it under water, and reported the incident and his tracker location, finishing with a heartfelt query about his wife. There was plenty of time for the whole message before the first words could reach the raft, and he waited patiently for an answer. The possibility that he might not be heard was something he would face later if he had to.

	The Box was typically terse.

	"The Cephallonians are on their way. I can detect Janice with confidence, but not the glider. When they reach your area, you will have to talk steadily so that they can home on your sound."

	"Then you can't tell me how close I am to her." Hugh was less patient with the inevitable pause this time, though he knew what the answer had to be.

	"No. I was able to associate her original call with a regular set of echoes from local wave sounds, and maintain an image. The submerged part of the sailplane reflects very little sound, and most of that downward, I expect. If you would care to get out and immerse yourself, talking all the time, and of course fastening yourself securely to the aircraft, I can probably resolve the problem."

	Hugh hesitated for only a moment. A five-hundred-kilometer water depth is, objectively, no worse to an Erthuma than fifty meters, just as a fifty-story fall is no worse than one of five. The trouble is that few Erthumoi are very objective even when scientifically educated. He spent several minutes doing careful things with rope, then eased himself out of the cockpit and let himself into the sea, holding on firmly to a wing in spite of his trust in the cord.

	"All right, I'm submerged," he reported, and began his favorite party showoff activity, reciting fragments of poetry in ancient English. The Box wouldn't care what he said as long as it got a continuous signal. He was declaiming, with gestures of his free hand, "These are Clan Alpine's warriors true, and Saxon, I am Roderic Dhu!" when the calm response reached him.

	"You're almost a kilometer closer to me than Janice, and getting closer at about two meters a second, presumably because of wind. Current should be affecting you both more or less equally on long-time average. There seems to be no emergency. The Cephallonians will reach you first but I would suggest that they go on and bring Janice back to the glider. I assume you will want it towed back here. I do not suppose you will want to repeat this attempt, but the structure represents much labor and material and some of it might be converted to other uses."

	Hugh said nothing. The Box was basically right, of course, but relief about his wife's safety and the experience of what was essentially another anticlimax had shut down for the moment both his enthusiasm and his imagination. Having the heroic rescuers leave the raft and the helpless rescued return was getting to be a little too routine. He had, of course, been perfectly right about the flying project, but it is small comfort for a pessimist to be right. Hugh got no satisfaction out of saying, "I told you so," especially to his wife. He would be very happy to tell how wrong he had been to Janice, the Cephallonians, and the assembled study authorities at Pwanpwan, once they reached the place.

	He shifted to old Welsh songs, which called for more attention and allowed less freedom to brood in spite of their usual subject matter, and kept broadcasting. Halfway through "Llwyn On," Thrasher—Hugh could tell the two apart at sight—surfaced beside him.

	"Shall I stay with you while Splash picks up Janice, or go along with her? You seem safe enough."

	"Sure, go along. Do I need to keep singing? You can see me on your own sonar now, can't you?"

	"We can, but your signal helps. Besides, the music is nice. See you in a few minutes." The swimmer vanished with no more splash than could be blamed on the choppy waves. Hugh, not used to having his voice praised and not entirely sure of Thrasher's sincerity—Cephallonians sometimes carried courtesy to the same extreme as many Erthumoi—shifted to "Ar Hyd y Nos." He knew only two verses of this and went on to comic songs in his own language. After all, Janice would be close enough to hear him shortly.

	Even with no trouble it took the rescuers several minutes to travel over a kilometer, get the woman into one of then-packs, and swim back. Several more were spent deciding that the Erthumoi would return in the glider rather than be carried, arranging tow lines, and getting under way. There was little talk at first en route. Both human beings were discouraged, and now that the tension of the flight itself was over, they realized how tired they were. While each wanted to cheer the other up, neither could think of anything very cheerful to say.

	They watched, silently at first, the rhythmic dolphin-style motion of the Cephallonians, and Hugh soon began to compare the vector problems of swimming with those of glider flight. Janice tried to sound interested as he began to talk about this and brighten up somewhat, but she found it hard to be sincere, much less enthusiastic.

	The tow was rougher than the flight, of course. Not only was the surface choppy, but every few seconds one wing tip or the other would either dip into the sea or be caught by a wave, adding a jerky yaw to the pitching discomfort. The Cephallonians had started out trying to do the trip quickly—after all, the glider was decently streamlined and drew practically no water—but gave up in a minute or two. They could stand the jerks on the tow lines themselves, but Thrasher was beginning to worry about pulling the frame apart. That, at least, was what he said; Janice muttered to her husband, "Kindhearted old fish, isn't he? I wish he could forget about my stomach."

	Hugh raised an eyebrow. "Don't you wish you could?"

	"It's all right with the diving juice gone. And no comments, please."

	Hugh had not planned any, and kept his face as expressionless as possible, since that part of his suit was transparent. Vectors were much more fun than arguments.

	And much more inspirational, he was beginning to realize, where practical plans were concerned. The glider experiment had not been a total success, but it had certainly not been a waste of time. The sailplane had been doing just what was asked of it, combining a vector directed away from where they wanted to go with one at right angles', working in a little basic Newton, and producing a resultant headed—yes. Even the labor and material that had gone into the aircraft itself should be useful—

	The man's carefully blank expression was gradually melting into a smile. Janice, seated ahead of him and watching the waves and the Cephallonians, as well as the change of tow line slack from moment to moment, did not notice.

	Hugh probably wouldn't have heard her if she had seen his face and asked him about it. By the time his expression reached grin level he was setting up nice, detailed, quantitative problems for The Box. Really detailed. There would even be a use for a thruster, as long as it were reliably turned off. That distracted him briefly; just what had gone wrong with the units Janice had employed on the sub? Why had they chosen to go wide open? They had turned off for her; did that mean it would be all right to use one of those four for his new idea, or would it be safer to take another? Or should something entirely different be improvised? He couldn't think offhand of anything else on the raft that would serve the purpose, but that didn't mean there wasn't anything.

	But that was a minor detail. He forced himself firmly back to the number of questions that only The Box could handle in reasonable time. By the time they reached the raft, Hugh Cedar was completely happy again and went straight to The Box.

	Janice understood the questions, of course, which she would have heard clearly enough even if their note recording units had not been interconnected. She was less happy than Hugh, not because she could see any serious flaw in her husband's new idea but because she hadn't been able to see one in any of the others, either. They had all been good ideas, but had simply run into unconsidered aspects of reality.

	And there is no way in the universe to be sure when all the facets of any situation have been viewed. Ordinarily, the woman would have been quite calm about this; it was her normal personality pattern, that of a scientist. In the last few dozen hours, however—well, Chaos had not exactly developed a personality in her mind, but she was beginning to capitalize its name mentally. This was emphatically not normal Janice Cedar.

	She remembered what had happened to Thrasher when he had passed his depth limit and she had had to use the conditioned command that Splasher had confided to her in order to rescue them both. Luckily, there was no such hypnotic suggestion implanted in her own mind that Hugh or one of the Cephallonians could use—at least, she considered it lucky. Erthuma minds didn't work that way. It would be a tempting explanation for the thruster incident, of course, if one were mystically inclined ...

	Janice brought her thoughts back to the job with a start. What was happening to her? Was she worrying herself out of sense and sanity? So Cephallonians had safety techniques Erthumoi couldn't use if they wanted to; human minds were different. Why should she worry about that? Especially, why should she worry about it now? All right, so she and Hugh would be starting another trip shortly, and the swimmers as usual couldn't go along. That was all. Don't fuss, woman.

	She came back to the real present. There had been no question of Cephallonians coming along. They couldn't. The problem was, how much of The Box could they take? The boat wouldn't carry the whole unit. A single module could handle the running calculations, but more would be needed to talk properly to the living crew and tell them what action the numbers demanded. The Box had no subjective disapproval, dislike, or fear of being taken apart, but even it wasn't quite sure how much of itself would be required for the journey and how much might be needed by the Cephallonians. There was no obvious reason why they would need any of it, as far as safety was concerned, but the swimmers naturally hoped to continue at least some of the planned study work. They were thinking beings; simply waiting to starve if their friends failed to reach help was no part of their plans. For one thing, someone— Cephallonian or Box—might come up with an explanation of the thruster failure, and it might become possible to send out something piloted only by another module. The Box was not hopeful and the Cephallonians, who distrusted artificial intelligence on principle, disliked the idea, but the possibility existed and feelings might change if a fermenter died.

	The glider had been modified, though not as radically as might have been expected. The right wing had been amputated two meters from the fuselage, now once more a hull. The fabric from the severed portion now covered the other surface of the stub. Hugh's original plan of mounting the wings to rotate on a single lateral spar had turned out fortunate; only minor changes in the rigging were necessary to make it practical now. One of the thrusters that had misbehaved for Janice was lashed firmly to the end of the shortened wing, after having the power lines from its fuser disconnected so that nothing could possibly turn it on—all hoped.

	After much discussion, most of the rest of the raft's sheeting was cannibalized to use as a covering for the bottom of the left wing; Hugh made an impassioned argument on the importance of symmetry and won without support from The Box, which was quite ready to allow for odd shapes in its calculations. The original cockpit was covered and a new one arranged so that the crew would be located both before and behind the left wing. Lines were rigged to let the wings be rotated on their central spars by the crew.

	And, finally, a four-module section of The Box was firmly lashed into the front cockpit, and Hugh's suit tracker plugged into it.

	The whole craft was easy to carry on Habranha, though walking was far from comfortable on the heaving raft. The Erthumoi got it over to the tank that had been vacated by the Cephallonians for the moment—if for some reason it didn't float, there was no need for a major salvage job over five hundred kilometers of water. The thruster proved heavy enough to do what Hugh had hoped; the stub of the right wing hung as nearly straight down and the intact left one pointed as nearly straight up as wind allowed. The new cockpits were now on top and the waterline of the floating hull safely below their edge. Hugh had had the foresight to improvise a bailer from scraps of wing covering but still felt uneasy about the roughness of the sea. There was a little sheeting left on the raft; after some thought, and rather more argument, he used this to seal off the interior ahead of and behind the crew stations. He hoped he had done a good job, since the new partitions would obviously prevent bailing even more effectively than they were likely to stop inward leakage. The Cephallonians weren't greatly bothered about the loss of the fabric; too little was left in any case to make the tank much of a shelter for them.

	The Erthumoi boarded, Janice in front as before. Wind pressure was holding them against one side of the tank; Thrasher activated several thrusters and turned the raft so the open end was downwind, and the boat drifted quickly away.

	The Module began ordering its crew to pivot first one wing and then the other as it computed the air and water currents from the tracker readings. The Erthumoi were not too surprised to find themselves moving across the wind— after all, they did not know the current direction. They did, however, see the waves, and Hugh quickly turned the hull so that these came bow on. There was no point in asking for a bailing job before it was necessary. The Module didn't seem bothered, and their actual direction appeared little affected after the wings were turned once more to offset the change in hull heading.

	For a quarter of an hour they maneuvered at seeming random, though the raft quickly disappeared in the distance. Then they approached a spout, and Hugh grew tense. He mentioned it to The Module, which had no sensory information but the trackers.

	"I inferred that," was the answer. "I am using the current toward it. We will pass it on the right, and gain more than a kilometer toward The Iris. The technique is very simple, but whichever of you is handling the air wing will have to be ready to respond quickly to orders. The water wing I can predict more readily." Hugh said no more.

	"Air wing thirty-five degrees to the right." Janice obeyed. "Overcontrolled. Two degrees left."

	"I can only guess at degrees," the woman pointed out.

	"Calibrate. Make some sort of marks on the control cords."

	"Of course."

	"Water wing, eleven degrees right."

	"Tell me when I've reached it," replied Hugh.

	"Close. Closer. Stop. Keep the hull at its present heading, whoever is handling the rudder. Are we dangerously close to the spout?"

	"About a hundred and fifty meters from the nearest spray," Janice replied.

	"Good. Hold all settings." There was a pause of over a minute.

	"Hull heading six degrees left, air wing six degrees right, water wing three degrees right." It took perhaps a minute and three or four corrections to establish the new setup, and by this time both living crew members were almost relaxed. They were starting to feel comfortable with the orders, and even with the results; Janice, watching her own trackers, reported that they were actually working their way more or less steadily along a fixed line from the raft. Hugh had to take her word for it, since his own inertial equipment was now part of The Module.

	In any case, he was having to spend much of his time bailing. The glider had ridden very high on the water and had shipped very little spray; with the weight of the thruster forcing the stub of the right wing to act as a keel, however, this was now less true. He hoped fervently that nothing was getting through the bulkheads he had improvised at either end of the cockpit. He told himself repeatedly that the Cephallonian adhesive was supposed to be very good, but did not say this aloud. Janice could be objective at inconvenient times.

	Occasionally the gain in distance was really impressive, as vectors combined to whip them around one side or the other of a spout. At other times human patience would wear thin as they crept one meter along the Iris-ward radius out of twenty or thirty along their current sub-Grendel circumference. Sometimes, even with The Module directing, they actually lost distance for a while. Neither was sure whether this was because there existed no useful vector solution at the moment or because one or both of them had been too slow following orders. Only The Module could keep real-time track of the constantly changing water and air currents, and only The Module could solve their angle problems quickly enough. By unspoken common consent, they did not ask their electronic companion who or what should be blamed, and it did not volunteer information.

	They had to sleep, of course. Janice allowed her husband to take the first watch, and carefully refrained from checking the time it started, so she didn't know how long he let her slumber. She had hoped to give him a full ten hours when his turn came, but a complication emerged.

	"Our drag component seems to be increasing," The Module remarked six hours or so into Hugh's sleep. "We originally averaged nearly six meters real advance toward The Iris for each hundred of actual travel through the water. This has dropped over the last four hours to about three per hundred." The woman thought briefly of taking care of the matter herself, since the cause seemed pretty obvious, but allowed common sense to override personal pride and awakened her husband. He, after hearing the report and agreeing with her, rigged another safety line to his suit and went over the side—Janice did not argue for the privilege—to spend several minutes removing a ten-meter-long banner of weed trailing from the bottom wing and the thruster. Much of it was charged, but his suit protected him, though flashes were visible from the surface even in daylight and caused Janice some uneasiness. He climbed back aboard, and insisted that he couldn't get back to sleep.

	By then the spouts were noticeably less frequent and the air clearer. Grendel could occasionally be seen, though still apparently almost overhead. It was obvious even without tracker data that they were working their way out of The Cataract into clear Pupil. This was the good part. Less comforting was the realization that they were now far beyond the range of the part of The Box that had been left on the raft, and that if any serious trouble developed there was no way the Cephallonians could know about it or find them.

	But even Janice had now shed the depression following the failed glider flight and was looking ahead optimistically. The boat was not leaking detectably, the bailing had been able to keep up with water slopping into the cockpit—Hugh insisted that the exercise was doing him good— and it was even possible that in another few hours they might be visible from orbit, though neither of them considered that a chance worth counting on.

	Wave and wind were much less chaotic; sometimes half an hour would pass between orders from The Module and two or three times one or another of the Erthumoi had been able to see for themselves slight departures from a fixed angle between their path and the now long and regular waves, and to make a correction without orders.

	"You know," Hugh remarked at one point, "this could almost be a sport. We should try it when we get home."

	Janice pursed her lips doubtfully for a few seconds, then shook her head negatively.

	"I don't think anything needing robot assistance could really be regarded as a game," she pointed out. "A sport is supposed to show your personal skill, isn't it?"

	Hugh shrugged. "I guess so. Just a thought."

	"Hull heading slightly left, no change in water wing, air wing two degrees right," came the commanding voice. "Slightly" had come to mean "as little as human senses will permit," and implied that several attempts would be needed before the electronic intelligence would be satisfied, so Hugh's full attention wandered from the conversation.

	Janice took time to eat, and spent a little more wondering whether their partial recyclers of their suits and the "cheese" they had brought with them would actually get them to The Iris. She was not worried, of course, just planning. They were likely to be seen by a native well before reaching the ring continent in any case—though whether the Habra would be interested was quite another matter. Aliens were no longer much of a novelty on the planet, they had both observed.

	On the other hand, it seemed possible that the vehicle they were riding might collect a crowd.

	Janice began glancing hopefully at the sky every few minutes.

	The routine was getting too boring to be a sport, even Hugh admitted.

	"Air wing two degrees right." Ten minutes' silence.

	"Hull heading one degree right." More silence.

	"Hull heading slightly left." This was at least more interesting, since it took more time and attention to satisfy The Module.

	"Drag getting too great. Clean the water wing again." Janice insisted on taking her turn at this, which was a harder job than it might have been; they had agreed not to use their knives, partly because of the risk of losing them irretrievably and partly to avoid chance of damage to the covering fabric. The weed had little mechanical strength as a rule, though sometimes a strand or two of the stuff they had used to build the hull frame would be involved. Several times, as a result, the knife discussion was reopened; saving time in clearing the growths might be worthwhile, since they always lost distance—blowing downwind and drifting down current back toward The Cataract—while someone was doing the job. The Module always advised against it, however, since there was no way to tell in advance what sort of material would have to be faced, a preliminary check would be time-consuming, and loss of a knife would be permanent.

	So boredom became the order of life, while Grendel shifted very slowly downward in the sky. Erthumoi are extremely bad at judging vertical angles and they had no measuring devices for such quantities, so knowing that they only had to bring the star down to about seventy-five degrees above the horizon was little help.

	More meaningful facts were that the near edge of Iris was about six hundred eighty kilometers from the center of The Cataract, that they had started some thirty kilometers from the center, and that the trackers claimed that they had made nearly a hundred kilometers radially while traveling nearly two thousand through water in a widening spiral around the heat pole. They had not kept very careful track of time; on Habranha there were no nights to serve as punctuation, its orbit was circular enough to make one part of the roughly three-week year just like another, and while Grendel's companion sun could be seen easily enough in the daylight sky if one looked for it and would with a little mental arithmetic provide a "yearly" calendar, neither had bothered. They had been roughly four hundred hours on the journey; their food was still adequate, and the Cephallonians should still be safe.

	But there was quite a distance yet to go, whether one thought of ideal vector or through the water.

	The sky was clear, now; they were in plain Pupil and out of The Cataract. The water too was clear except for life. The next major change would be near the end of the voyage, when silt from the melting Iris would start to discolor the ocean. The natives salvaged what silicate they could, of course, but rivers in the melting ice stole a good deal of the finer material in spite of their efforts.

	There was no sense looking for this for a long time yet, but both Erthumoi did glance at the sea more frequently than common sense dictated. Whenever one of them went over the side to clear weed he or she found it increasingly hard to feel sure that the water wasn't just a little murkier than last time ...

	It occurred to Hugh, after another couple of hundred hours, that they might not have to go even that close to The Iris; there would be salvaging subs trawling for silt fairly well out in The Pupil, and fishers even farther, and one of these might easily spot them. If it did, it would certainly investigate. Their craft would certainly be a very peculiar sight to Habranhans either optically—the winged natives could see, of course—or on sonar. There was no point using their transducer to call for help, of course, since the natives sensed radio and would not, unless regularly dealing with aliens, be equipped to receive or transmit sound.

	There was no way the Erthumoi could attract native attention. Not deliberately.

	They were still nearly four hundred kilometers from the nearest shore of Iris, though they had made several widening spiral journeys around The Cataract as they stole their tiny increments of radial distance from each kilometer of sailing, when the polymer skeleton of a native submarine drew up beside them.

	The crew, of course, were all armored and saturated with their own type of diving fluid. Apparently they were not equipped with sound devices, but they looked the aliens over for several minutes, made gestures that the Erthumoi assumed to be the equivalent of friendly waves, and drew away again. They seemed not to recognize the situation as an emergency as Janice and Hugh vigorously waved back.

	"Now what?" asked the man as the craft disappeared.

	"The wind and current are both weaker, but they both still set toward The Cataract. The choices seem to be to keep on working or give up and drift back where we came from," Janice replied. The man had nothing better to offer, even in his thoughts. The realization of how much better they would have done with a hull that didn't catch wind or current had struck him long ago, but so had the futility of mentioning it.

	They continued to follow instructions from The Module but routine changed somewhat for a while. Six more times in the next four hours a submarine appeared near them, remained for a minute or two while its crew, resembling six-winged dragonflies but too heavy in their armor to fly, looked them over, gestured in what appeared to be unsurprised and casual friendship, and went on its way. None of them appeared equipped to communicate with aliens. Both Erthumoi wondered why the first to find them had not broadcast the news, and how long it would take before someone really helpful would show up.

	"I suppose," Janice said at last, "that the first one did report. Probably no one working in The Pupil expects to run into visitors; these others have been just people who got the word and wanted a look. The help won't get here until news reaches The Iris and someone who knows about our study group."

	"Maybe." Hugh was a little doubtful. "Habras aren't usually just curious about aliens; most of them have seen us by now—they fly, remember, and have one worldwide culture. I'd have expected these other subs to have come for some different reason, but I can't guess what it was. I suspect we'll just be waving to them until someone from Inex or higher hears the story and gets here."

	"They've all seen us, but they haven't seen a boat like this," his wife pointed out. "I'd want to look over something this odd in a lot of detail myself.''

	"Well, maybe. The vector principle it uses should be obvious enough at a quick look, though. We'll see."

	What they saw after the seventh visit was more hours of boredom. There were no more submarines, just travel. There were occasional—very rare, now, as they emerged into the least chaotic area of Habranha's ocean—orders to change a wing setting, but increasingly frequent demands that one of them go overside to clear weed.

	This, they knew, would get even worse as they approached the ring continent. Silt from its endlessly melting inner edge enriched the water and supported a gigantic food pyramid. The natives did their best to conserve the silicate, which they brought at great labor and expense from the ocean bottom to fertilize the relatively clean ice of The Iris and let them grow food for themselves; rivers of meltwater flowing into The Pupil encountered beautifully designed and built dams and sediment traps. Still, lots of the fine stuff got away, and the natives had to make the best of it by fishing the teeming waters of the central ocean. Presumably it was fishing submarines that the Erthumoi had seen.

	But now these ceased to appear, and hour after hour went by with nothing to relieve the boredom but an occasional trip overside.

	Even the thunder of The Cataract was gone, though not the higher-pitched rush of wind and wave, so when the helicopter did come the couple heard its rotor beat long before they saw it. When they did, it was not directly between them and The Iris, and not heading directly toward them.

	They waved and even shouted, knowing that both actions were futile against a wave and spray background, and watched with mounting tension as the aircraft went on past.

	Then it shifted course roughly toward them. Only roughly; it flew by again. Then it hovered, a kilometer away, and Hugh, rising as nearly to his feet as he dared, caught glimpses between the waves of the upper part of a native submarine below the flyer and heading directly toward them.

	Then the crew of the helicopter seemed to see their boat, and the machine swelled in their vision. A few seconds later two heavy-duty slings were descending toward the Erthumoi.

	Hugh reached for the nearer sling and started to hook it to his suit. A thunderously amplified voice, speaking his own language, stopped him.

	"Around your hull! We've got to get that public nuisance out of the water!"

	"Why?" asked the man, quite reasonably. Janice went silently overboard with the other sling and began to adjust it.

	"Tell you later! Just do it! The Habras are polite people, but in their place I'd be working up an interstellar incident. Get moving!" Hugh was still inclined to stay where he was and try to figure out why his beautiful, well-planned, and successful vector boat was a public nuisance to anyone, but Janice added her voice to the one from above. Thirty seconds later the rotor hum rose in pitch and their hull lifted gently from the surface. The bottom wing followed, trailed by the several meters of weed that had accumulated since they had last cleared it. Habras on the submarine, which had also approached, gestured, and their craft settled out of sight.

	The Erthumoi climbed a ladder that had been lowered from a hatch of the flyer, and found themselves surrounded by half a dozen of their own species. Hugh, quite able to put first things first when they were important, reported where, why, and in what condition they had left their Cephallonian companions. The aircraft commander nodded.

	"We'll pass that on to the natives. Their subs can probably tow the raft out, and we should certainly let them try first. If they can't make it, someone can design and send in a better raft."

	The Cedars nodded. There was little risk of Habranha natives developing an inferiority complex from their alien visitors, both knew, but the policy was basically a good one. It sometimes kept starfarers from getting too arrogant.

	"I suppose," the aircraft commander went on, "you've figured out by now why we had to get your boat out of the water." The fellow glared at him, and Hugh had a feeling that he himself should be blushing. A glance at his wife provided no help; she evidently didn't get it either, which was some comfort. The pilot waited only a moment. "That thruster you had on the underwater fin or whatever you call it is made of metal, which is very rare on Habranha. It had gathered weed, much of it highly charged, so it's—"

	"It was broadcasting!" Hugh was just enough behind his wife to be slightly out of phase.

	"It was, according to the Habras, howling. It was making conversation impossible for forty or fifty kilometers around, even under water. What it would have done if it had been producing the same waves above the surface I hate to think, but thank reason for impedance mismatching."

	"But why so far? Water doesn't carry low-frequency electromagnetics very well," Hugh objected.

	"When the waves stimulate discharge in electrical organisms, simple attenuation formulae don't work," the captain pointed out gently. "But why was the driver mounted so far down? I can see it isn't working now, but when it was, it must have tried to lift your front end right out of the water—or was that the idea?"

	Janice smiled. Hugh could get some of his own back, here.

	"Oh, no." Her husband shook his head firmly. "The driver was never working at all." Would he explain why? she wondered briefly. Of course not. At least, not completely. No one had figured out yet what had made the thrusters unreliable, unless Thrasher or Splasher had had an inspiration since the Erthumoi had left. Inspirations did sometimes happen to people. But Hugh was quite good at covering.

	"We were just using it for its weight," he went on. "We didn't have anything else heavy enough that we could afford to risk—nothing at all except our robot and equipment, and we needed weight to keep the wings of our vector boat vertical. If the thruster had been pushing, as you say, we'd have wanted it right up under us. Besides"—he caught Janice's eye briefly—"if we'd been using it that far below the hull we'd have had to rig a line to control it with. Can't you imagine what would have happened when that began to pick up weed—at high speed? More drag on the line, more pull on the control; if pull meant more power, then more drag, more speed, more speed, more weed—you've heard of feedback, haven't you?" Janice kept a straight face, too.

The End