By Hal Clement

Mesklin is the single "planet" of 61 Cygni A, the brighter member of a binary system approximately eleven light years from Sol and Earth. While several times as massive as Jupiter, it is not a gas giant; like Earth, it lost nearly all its hydrogen during formation. Predictably, most of its mass is concentrated in a core of degenerate matter, and its total volume close to that of Uranus or Neptune.

It has attracted astrophysical attention since its first well-resolved images were obtained, for several reasons.

First, shape. It is close to rotational instability; with a day of less than eighteen minutes, its equatorial radius is more than twice the polar one. Inertia gives it an equatorial surface "gravity" only three times that of Earth; the polar regions, lacking centrifugal effects and far closer to the ultradense core, would flatten a human being under several hundred times his normal weight.

Second, physical nature. The original accretion heat has been lost completely enough to leave the surface temperature at roughly radiational equilibrium; the oceans are principally liquid methane, the atmosphere nearly all hydrogen with a surface pressure of about eight bars. It is not clear why settling of mantle mass has not increased its spin rate for the last few billion years so as to cause general breakup and forestall the development and normal evolution of life. (The planet has several rings, which might possibly have formed from such an event; but rings don’t ordinarily last for eons.)

Nevertheless, physicists rather than planetologists had most to say about its original detailed investigation. A remotely controlled spacecraft was landed at the south rotation pole to conduct experiments in the hitherto unattainably intense gravity field there. Much information was transmitted to the researchers at a base on the inner moon, Toory, and much more was expected to be obtained on physical records when the craft returned. Unfortunately, it failed to respond to the liftoff command, causing extreme consternation to researchers of some ten worlds whose people had contributed to the project.

However, a sop had fortunately been tossed to the planetary specialists and biologists in the form of a manned observing station near Mesklin’s equator, where human and similar beings could, with precautions, stand the gravity for a time. Citylike patterns had been observed, with some uncertainty, in the mid-latitudes; and while there was little reason to hope that beings evolved for such conditions would be found anywhere near the equator, efforts involving firework displays and extremely loud sound broadcasts had been made to attract their attention.

These had been surprisingly successful. Barlennan, a sailor-trader-explorer of Mesklin’s seas, had discovered the station. Charles Lackland, sole staff member of the outpost, had managed to make linguistic contact and, after much effort, teach some of his own language to Barlennan and learn some of the latter’s Stennish.

At the start of Mission Of Gravity, a bargain had been worked out. Barlennan’s crew would travel to the south polar regions, and try to salvage as much as possible of the information in the grounded rocket. They were physically able to stand even the extreme gravity of the planet’s poles; their fifteen-inch-long hemicylindrical bodies, supported on numerous stubby caterpillarlike legs, were tough. They were neither arthropods nor vertebrates; their flesh was resilient enough to need neither internal nor external skeletons. They did not breathe in any usual sense; their energy was derived from reducing highly unsaturated hydrocarbons and similar compounds with atmospheric hydrogen, and they were physically small enough for adequate supplies of this gas to reach their extremely small body cells by diffusion. Their ability to use oral speech stemmed not from modified breathing apparatus but from evolved organs originally corresponding to propulsion jets like those of terrestrial cephalopods.

The season was propitious; the deal was made near the end of the brief winter, and Mesklin’s southern hemisphere midsummer nearly coincided with the periapsis of its orbit, so much of the journey would enjoy daylight (Mesklin’s year is some eighteen hundred Earth days in length, and its orbit quite eccentric).

The Bree, Barlennan’s ship, was a mosaic of individual rafts equipped with sails and centerboards, and represented a fair example of his species’ technological status. The ability of Lackland and his fellows to travel through the air aroused several different emotions in the captain, largely acquisitive and envious ones. He was perfectly honest by his own standards, but hoped to pry large amounts of usable, and saleable, know-how from his customers while carrying out their wishes–knowledge which he at first took for granted the Flyers would never supply willingly, and certainly not freely.

The trip to the pole involved first a long overland journey to an ocean strange to the Bree’s crew. This was managed by towing the vessel behind a tanklike vehicle driven by Lackland. During this stage of the mission, the Bree personnel encountered a number of adventures which put serious strains on their normal conditioning to avoid either falling, becoming vulnerable to falls by climbing, or allowing anything to fall on them. Events even opened their minds to such concepts as throwing.

Having to climb to the top of the tank to escape rocks being rolled downhill on them, with essentially no time to debate the choice, was a typical experience. A more extreme one was provided when the tank’s progress was blocked at the top of a cliff extending indefinitely in both directions across its path, forcing Bree and crew to descend somehow. The sight and sound of a nearby waterfall did not help Mesklinite feelings.

By the time the ship and crew had been lowered by block and tackle, raft by raft, to the ground below, reassembled, and refloated on the river fed by the waterfall, none of the crew members was as he had been. Whether any of them, Barlennan and his first mate Dondragmer included, was still sane by Mesklinite standards was debatable.

But at least the river led to the right ocean–the Flyers could assure them of that–and all were willing to go on. Lackland had to turn back, since there was no way to get the tank down the escarpment, but he had provided the natives with a number of communication sets complete with cameras. These could be used to talk with the Flyers on Toorey, and allow the latter to give advice and to see what Barlennan and the others were encountering.

But even at sea, familiar as it should be, there were disturbing experiences. The sailors were used to storms, of course, and even knew why ships should stay well away from any land during them: ocean level, even in high-gravity latitudes, rose enormously in the extremely low-pressure centers of such disturbances, due to the tremendous Coriolis force. A ship could find itself stranded surprisingly far from liquid when things had quieted down. Avoiding land on an unknown ocean, however, was difficult even with help from above, and at one point while at the still-low seven-g latitude, the Bree found itself floating on a pond in a valley drained by what had once more become a narrow streamlet almost surrounded by low hills–low by Flyer standards–on a presumably not-too-large island.

The local inhabitants proved to be of their own species, but they flew. They used gliders, launched by elastic cables, kept aloft by their pilots’ knowledge of wind patterns. Here Barlennan began to realize that the Flyers were at least sometimes willing to supply him with knowledge if he needed it. They explained how the gliders worked, though using seagulls as an analogy proved ineffective, and helped with still more information when disagreement with the locals made an escape necessary. Dondragmer was able to grasp the concept of, and to build, a differential hoist to remove a group of deep-driven stakes barring the Bree’s course downstream to the sea.

At still higher latitudes, the thin-walled dugout canoe which Barlennan had acquired along the way and was using to tow supplies collapsed and sank from second-order gravity effects, and once more the Flyers proved willing to explain, this time with no real emergency apparently involved. The Mesklinites already had a general grasp of Archimedes’ principle, of course, but would probably not by themselves have figured out the effect of rising hydrostatic pressure near its keel on the displacement of the "hollow boat."

The travellers eventually reached the south polar continent, worked their way up a broad estuary and its source river to a point only a few miles from the grounded rocket, to find their way blocked by another cliff–almost perfectly vertical and some three hundred feet high.

They were at the bottom this time.

Observation from space indicated that the escarpment completely circled a continent-sized area, and sent the planetary physicists arguing fiercely how any such phenomenon could have occurred under hundreds of gravities. This did not help the mission.

Observation from above showed one break in the cliff some hundreds of miles farther up the river. The ship was tacked up to this site, finding a region where the escarpment had collapsed (why only here, people wanted to know). Barlennan and part of his crew worked their way up slope and across the boulder-strewn continent above, while the Bree and the others went back downriver to wait at the point nearest the rocket. The crew above finally reached the cliff top above this spot, and set up block-and-tackle connection with the ones below as had been done with the first cliff long before.

They then moved themselves and supplies to the site of the rocket itself–which towered far above them. Because of the gravity, it would have to be disassembled and each part removed and studied from the top. The Mesklinites solved this final problem by spending many, many days burying the probe. Eventually they could reach its nose cap and start removing module after module, with no serious risk to the pieces by dropping them, under instructions from above.

At this point Barlennan renegotiated the contract, insisting on unrestricted access to any scientific information the aliens could supply. The aliens, after convincing him that at least some of this knowledge would be beyond his grasp without a long period of basic instruction, agreed to start the latter–and they agreed much more easily than Barlennan had really expected in spite of the events along the journey. He was a little disappointed that it had been so easy; but Dondragmer, a basically curious being, was not bothered in the least.

Salvage and schooling began together, and went on for many thousands of Mesklin days. Mission Of Gravity ended with the launch of the second Bree–a hot air balloon.

Under starts some thousands of days later still, toward the end of Mesklin’s southern-hemisphere summer, with the dismantling of the spacecraft almost completed, and the planetary physicists pushing hard for a return trip to the equator by ocean. They badly want the Bree to carry an inertial tracker salvaged from the rocket. The thought of the information about Mesklin’s interior which should be obtainable on such a trip, with observations from space permitting the separation of inertial and gravitational data supplied by the tracker, is affecting the dreams of human and nonhuman researchers alike.

That looks all right. Come aboard, Cookie. Then reach out and light it. Hars, lift–now!"

Neither crewman acknowledged the orders verbally; they acted. Karondrasee whipped aboard in normal centipede fashion, scooped a coal from the lifting fire into the long spoon waiting for the purpose beside the furnace, reached through the handiest crenelation in the Bree’s mostly solid gunwale, and steadied the burning fragment over the frayed-out end of rope fuse beside the basket. He was’t bothered by the form of address; there was need for haste, "Cookie" was shorter than "Flight Engineer," the duties overlapped heavily, and he was filling both of them. He was, however, annoyed and uneasy for other reasons; he had had to spend many days treating the three lengths of cord with meat juice and, as he saw it, wasting two of them. As cook of the old Bree’s crew he was used to seeing the results of his labors vanish, but he disliked seeing them burn up. That was the annoying part.

He was uneasy as well, because things might not work this time as they had on the two test burns. The first had not been dangerous, of course; it had simply served to show whether his juice treatment would really turn rope into a useful fuse. That sample was short enough to need only a day or so to make.

The second test should either not have worked at all or produced a simple, harmless fire fountain. By doing the latter it had encouraged everyone. Now the third and potentially most dangerous trial was under way.

The captain seemed unsure, too. He was watching the fuse as closely as Karondrasee was. So was Sherrer.

Hars was not. He was tending his lifting fire and eyeing the tensely swollen bag of the third Bree. He knew enough about the present test to want the ship to lift quickly, but if it rose too quckly, that would of course be the captain’s fault. Hars was obeying orders.

That last thought was also in Barlennan’s mind, and he was watching the delivery of the bit of fire tensely. If he had given Hars his order too soon–

Strictly speaking, he had. He felt the basket’s deck stir under him, and saw the figures on the Flyers’ instrument change. He would have stopped breathing for a moment if he had been a breather. Karondrasee, however, also knew the plan, knew what would have to be done if the fuse failed to light, and certainly didn’t want to get out and push the coal to the right place while the balloon rose without him. As he saw his spoon rising slowly from its target, he tipped it over without waiting for an order.

No one actually saw the coal drop; falling, here, was much too fast for even Mesklinite vision. Cook and captain did see, as the air below it was compressed enough to speed its combustion rate by perhaps an order of magnitude, a sudden flash on the ground half an inch to one side of the fuse end. Before either could comment or even curse, the rope ignited–apparently from radiation, but conceivably from a flying spark, though neither witness could vouch for the latter. They didn’t really care; the wadded rope-end was starting to glow, and that was all that mattered.

"Lighted all right?"

"Yes." Barlennan didn’t bother to look at the block of polymer from which the question had emerged. "Hars, up as fast as you can. Never mind checking wind. I’d like to keep on this side of the rock to see what happens, but getting to the other may be safer and staying out of reach will be safest of all. I wish someone knew what ‘out of reach’ was, but if we do blow that way, up will mean a lot more than sideways."

"Right, Captain. Up it is."

Up it was. Not rapidly; it took a lot of lift to start an upward motion near Mesklin’s south pole, even though once started acceleration tended to be high. That was why more than a thousand feet of fuse had been laid out, and the original test of its burn rate had been made.

"Please keep this eye aimed at the rock, wherever we go."

The block spoke again.

"Right. Sherrer will see to it," the captain responded, still without looking at the communicator. "We have you blocked up far enough to look over the rail already, and he’ll wedge the back up more if it’s needed."

"Are you set to turn it too, or will it be easier to rotate the whole balloon?"

"Much easier, though it’ll cost a little lift. It will also make it unnecessary for you to look across the fire. Don’t worry yet, it should take half a day to burn down."

"I never worry. I just wonder." Jeanette Parkos, who had taken up Charles Lackland’s communication duties when health had forced him to return to Earth, was rich in comments like that. She had greatly improved Barlennan’s Spacelang in the last few thousand days, and to his surprise and in spite of her alien hearing and vocal limitations she already spoke Stennish much more fluently and clearly than her predecessor ever had.

"I’d appreciate a bit of down tilt whenever Sherrer can provide it," she now suggested. "I can’t see up to the horizon, but I can’t see down enough for anything within a couple of miles, either. You’re a lot closer to the rock than that, according to the tracker readout, and I hope you’re closer still when it goes. I sometimes wish this thing had a wider field of view. Of course, I sometimes wish it could zoom closer, too."

Barlennan was not entirely sure that he shared the hope, though he wanted a good view himself. The Flyer was on Toorey, Mesklin’s inner moon. Her communicator would let her see what went on. The closer to the rock the better for her, but nothing could, presumably, happen to her at that distance. Barlennan lacked both the distance and the seeing equipment, and wasn’t sure which he missed more. The Flyers had assured him that there couldn’t possibly be enough energy in the propellant cell now being tested to lift the rock above it any significant distance, but the Flyers had been wrong before. He remembered vividly the Foucault pendulum fiasco; they had been certain it would give a convincing demonstration, this close to the pole, that Mesklin rather than the sky was doing the spinning. Unfortunately no one, native or alien, had been able to observe the six-inch pendulum’s plane of motion; its period was too short, and like any tuning fork its vibration had been damped out by the air a few seconds after it had been started.

They had all heard it, of course.

None of the Flyers seemed to remember that now. Barlennan had not seen an explosive in action since Lackland had used his tank’s gun so many thousands of days before, since the previous cell test had produced only the hoped-for fire fountain; but he had been told in detail how such substances were used elsewhere in the universe. These accounts, and a vivid memory of the effect of the shells Lackland had used, left him wondering why no one seemed to worry about the behavior of pieces of the rock. Unlike Jeannette, Barlennan was a rather efficient worrier; he had not raised the question with her because he knew the aliens were extremely knowledgable in spite of their occasional slips, and he still didn’t like to look ignorant. Answers beginning with "Of course" bothered him, especially in front of his crew, most of whom were now fairly fluent in the alien common language.

"Can you tell if it’s still burning, and how far it has to go?" the Flyer queried.

"’Fraid not. The fire doesn’t give any light to speak of by daylight. Too bad there’s no night now–though if there were, we’d have to plan pretty tightly so the fire would reach the cell by daylight and we could see what happens to the rock."

"It might have helped, but since we couldn’t be sure just when the fuse would run out–well, it’s academic anyway. Even if you could control your landing point well enough you’d probably not have time to get there now, get out, cut the fuse, and start over. We’ll just wait and hope. Good work, Sher; I think I see the rock now, though I can’t be sure it’s the right one. It looks like the pictures we got before, but there are such a lot of them–rocks, I mean–this close to the edge of the plateau that I could be wrong. Too bad that fuse doesn’t smoke."

Since cooking fires on Mesklin don’t normally smoke either and other kinds of fire are extremely rare, some minutes were used in explaining the last word; but someone remembered the Stennish for "fog" eventually, and there remained an unknowable length of suspense time when interpretation was managed. The earlier tests had given the Flyers some idea of the fuse burning rate, but the two had disagreed by over ten percent. Tension mounted, therefore, as the minutes passed.

Especially for the captain, as Bree Three was drifting toward the rock, keeping Sherrer busy and Barlennan worried. Their height should be great enough now to be pretty safe provided the aliens hadn’t overlooked anything important, but there was no way to be sure they hadn’t.

And, in fact, they had.