Hal Clement - Noise

The masthead made another report. “There’s a little more ice showing in what’s just come up.” There was a brief pause, then, “’Oloa says we all should see that the ice is denser than the other stuff, and says I should be able to tell her why the big lump turned over. I can’t, right now. How long do I have before I lose points?”

“At least an hour after one of us figures it out,” Wanaka answered promptly. Then she added, “And if that takes more than ten minutes, you don’t lose any.” The doll’s voice could just be made out in a momentary pause in the thunder, but its words were indistinguishable to Mike. If they carried any meaning to the captain, she did not relay it.

It was evident that there was no use trying to dodge all the flotsam. If it were going to do any damage, it had probably already done it. Keo, at the captain’s orders, got under way again, though very slowly indeed—they were still avoiding the larger collections of ice and coral. The city, which it probably wasn’t, still floated with its near side about half a kilometer away, and a trader would no more forgo a closer look than would a scientist.

The fine bits of coral were everywhere; there was no avoiding them. The larger chunks of ice-coral mixture, many up to ten meters across, were no problem. Twice, as they passed close to one of these, it turned itself leisurely over; the roughly spherical shape was starting to seem reasonable to the adults, but well over ’Ao’s allotted hour had passed before any of them actually worked out the cause. As usual, it was embarrassingly simple. Keo, for good reason, saw the answer first.

He was still at the helm, and had been watching a particularly large chunk for many minutes, since their course lay quite close to it. It slowly dawned on him, as they neared, that it was not now turning over but was, very slowly indeed, rising . There was more of it out of the water than had been the case five or six minutes before. Then as Mata reached the nearest point to it on her course, the turnover started with unusual speed. This time, again, the near side was rising, and without waiting for orders the mate steered even closer. Wanaka seemed about to say something, but apparently decided to trust the helmsman.

He used voice, and his tone held satisfaction.

“I get it. I see what ’Oloa meant. The ice is denser, and of course the part under water melts faster. The body rises, and its center of gravity rises faster because it’s the part under water that’s losing weight. When the center of gravity gets higher than the center of buoyancy, it has to turn over. Anyone who’s ever planned a boat knows that. Since the things aren’t perfectly round, and probably don’t have the same density all through, they don’t always tip in the same direction or by the same amount.”

The others nodded slowly, and Wanaka called the information up to the masthead. ’Ao, while long since relieved from the worry about losing points, was audibly annoyed at not having worked the answer out for herself. She had, after all, been taught the relevant physics, like anyone who would be expected to spend her entire adult life between floating cities and boats.

They had reduced their distance from the “city” to a few hundred meters when the child restored her own self-respect.

She called a question down from her perch. It was carefully not worded as a warning or even a question, of course, but it deflected the thoughts of all three adults onto an interesting line.

“I wonder how often this big thing turns over…and which way is next.” Wanaka and Keo reacted, but not verbally.

The basic wind was still fairly strong at this latitude, but its direction was inconvenient. Keokolo had to tack several times. He also made skillful use of the more or less random gusts around two local storms, in a maneuver that Mike thought of as slingshotting; but it was over an hour before they were out of the thickest part of the flotsam. Even then, three of the crew felt a little uneasy whenever they looked back at the huge drifter; their line of sight was still uncomfortably upward. That was unusual on Kainui.

Wanaka looked straight back, without any upward component to her line of sight, and a frustrated expression showed around her mask.

“Well, it can’t be a city, but there’s a lot more there than ice. I wonder what it would be worth?”

“We could wait until it does roll. Then there’d be plenty of time before it happened again,” suggested ’Ao.

Wanaka did not respond to this suggestion, leaving both Mike and the child wondering whether or not it had been silly enough to cost points.

She also said no more about the forty-five-degree latitude limit. She had managed to scoop up several bits of the floating coral without destroying them, and spent hours during the next days as Mata was borne southward in examining them as closely and thoughtfully as possible. Sometimes she did this alone, sometimes she consulted with Keo or even Mike. ’Ao stayed at the masthead most of her waking time, since in a sense they were under way.

The ship’s equipment did include a small magnifying lens. This had failed to reveal individual grains of the still unknown metal powder, but did make barely visible the separate cells in the coral that apparently held air for flotation but which shattered completely all the way through a particular specimen if given even a slight excuse. The gas might not, actually, have been air, they all realized; destroying one under fresh water—the captain decided the knowledge might be worth the use of that commodity—produced sinking dust motes and rising bubbles, but there was no way to tell what either might consist of. If the solid was at all like any coral she or Keo had seen, it was probably some form of the carbohydrate-protein copolymer that even Mike understood composed lobster shells at home. All the adults could think of ways to measure the density of the dust and become more certain about this, but sadly all the ways needed delicate weighing equipment that was not to be had. Mata , like her parent, was a cargo craft rather than a research vessel. The seed from which she had grown had plans for a basic ship only, with only basic equipment. The seed had not reproduced itself; it had been provided by the original ship-growers as part of the original sale, quite expensively as Wanaka had plainly remarked once or twice. Mike, after hearing the captain describe the deal, had come to regard the seed as a sort of limited warranty, which had now expired. Without actually worrying, he now did feel a little more conscious of the personal risks he had casually accepted.

Another of the huge floating mysteries was sighted in the next few days. Wanaka steered Mata as close as even she dared, but that was not enough to let them see any significant difference from the first one. ’Oloa, on request, reported that they were just forty-five degrees from the equator, plus or minus its—or her, as Mike was beginning to think—current accumulated three-minute uncertainty, but Wanaka said nothing more about working back to city latitudes. Keo asked no questions, and Mike of course followed—or possibly had furnished—this example. ’Ao, he had decided, really didn’t care in the least where they went or how long they took, as long as she could earn an occasional few points toward adulthood. She was not exactly kept at the masthead by orders, but knew it was the most likely place to spot something useful. She would descend to eat, sleep, and salvage hailstones for the water breakers, or to sweep the deck clear of them if these were full, but that was about all. Her conversational needs seemed to be satisfied by the doll.

Kaihapa, the twin world, was now almost at the western horizon. Kainui’s low haze made the other planet’s equatorial cloud belt—it matched climate zones closely with its slightly larger sister—almost indistinguishable; the crew now had to look through too much of their own world’s atmosphere. Its polar regions, where, as on Kainui, floe ice accumulated and raised the local albedo, were also hard but not impossible to distinguish. The apparent location of these features gave a very rough confirmation of Mata ’s latitude, of course, but ’Oloa was much more reliable. Now that Mike had learned the doll’s nature and purpose, it—she—was frequently consulted.