Mission of Gravity

XV: HIGH GROUND

The change of mind that had so affected the Bree’s crew was not temporary; the unreasoning, conditioned fear of height that had grown with them from birth was gone. They Still, however, had normal reasoning power; and in this part of their planet a fall of as much as half a body’s length was nearly certain to be fatal even to their tough organisms. Changed as they were, most of them felt uneasy as they moored the Bree to the riverbank only a few rods from the towering cliff that barred them from the grounded rocket.

The Earthmen, watching in silence, tried futilely to think of a way up the barrier. No rocket that the expedition possessed could have lifted itself against even a fraction of Mesklin’s polar gravity; the only one that had ever been built able to do so was already aground on the planet. Even had the craft been capable, no human or qualified non-human pilot could have lived in the neighborhood; the only beings able to do that could no more be taught to fly a rocket than a Bushman snatched straight from the jungle.

“The journey simply isn’t as nearly over as we thought.” Rosten, called to the screen room, analyzed the situation rapidly. “There should be some way to the plateau or farther slope whichever is present — of that cliff. I’ll admit there seems to be no way Barlennan and his people can get up; but there seems to be nothing preventing their going around.” Lackland relayed this suggestion to the captain.

“That is true,” the Mesklinite replied. “There are, however, a number of difficulties. It is already getting harder to procure food from the river; we are very far from the sea. Also, we have no longer any idea of how far we may have to travel, and that makes planning for food and all other considerations nearly impossible. Have you prepared, or can you prepare, maps with sufficient detail to let us plan our course intelligently?”

“Good point. I’ll see what can be done.” Lackland turned from the microphone to encounter several worried frowns. “What’s the matter? Can’t we make a photographic map as we did of the equatorial regions?”

“Certainly,” Rosten replied. “A map can be made, possibly with a lot of detail; — but it’s going to be difficult. At the equator a rocket could hold above a given point, at circular velocity, only six hundred miles from the surface — right at the inner edge of the ring. Here circular velocity won’t be enough, even if we could use it conveniently. We’d have to use a hyperbolic orbit of some sort to get short-range pictures without impossible fuel consumption; and that would mean speeds relative to the surface of several hundred miles a second. You can see what sort of pictures that would mean. It looks as though the shots will have to be taken with long-focus lenses, at extremely long range; and we can only hope that the detail will suffice for Barlennan’s needs.”

“I hadn’t thought of that,” admitted Lackland. “We can do it, though; and I don’t see any ‘alternative in any case. I suppose Barlennan could explore blind, but it would be asking a lot of him.”

“Right. Well launch one of the rockets and get to work.” Lackland gave the substance of this conversation to Barlennan, who replied that he would stay where he was until the information he needed was obtained.

“I could either go on upstream, following the cliff around to the right, or leave the ship and the river and follow to the left. Since I don’t know which is best from the point of view of distance, well wait. I’d rather go upstream, of course; carrying food and radios will be no joke otherwise.”

“All right. How is your food situation? You said something about its being hard to get that far from the ocean.”

“It’s scarcer, but the place is no desert. We’ll get along for a time at least. If we ever have to go overland we may miss you and your gun, though. This crossbow has been nothing but a museum piece for nine tenths of the trip.” “Why do you keep the bow?”

“For just that reason — it’s a good museum piece, and museums pay good prices. No one at home has ever seen, or as far as I know even dreamed of, a weapon that works by throwing things. You couldn’t spare one of your guns, could you? It needn’t work, for’that purpose.”

Lackland laughed. “I’m afraid* not; we have only one. We don’t expect to need it, but I don’t see how we could explain giving it away.” Barlennjui gave the equivalent of an understanding nod, and turned back to his own duties. He had much to bring up to date on the bowl that was his equivalent of a globe; the Earthmen, throughout the trip, had been giving him bearing and distance to land in all directions, so he was able to get most of the shores of the two seas he had crossed onto the concave map.

It was also necessary to see to the food question; it was not, as he had told Lackland, really pressing, but more work with the nets was going to be necessary from now on. The river itself, now about two hundred yards wide, appeared to contain fish enough for their present needs, but the land was much less promising. Stony and bare, it ran a few yards from one bank of the stream to end abruptly against the foot of (he cliff; from the other, a series of low hills succeeded each other for mile after mile, presumably far beyond the distant horizon. The rock of the escarpment’s face was polished glass-smooth, as sometimes happens even on Earth to the rocks at the sliding edges of a fault. Climbing it, even on Earth, would have required the equipment and body weight of a fly (on Mesklin, the fly would have weighed too much). Vegetation was present, but not in any great amount, and in the first fifty days of their stay no member of the Bree’s crew saw any trace of land animal lif e. Occasionally someone thought he saw motion, but each time it turned out to be shadows cast by the whirling sun, now hidden from them only by its periodic trips beyond the cuff. They were so near the south pole that there was no visible change in the sun’s altitude during the day.

For the Earthmen, the time was a little more active. Four of the expedition, including Lackland, manned the rocket and dropped planetward from the rapidly moving moon. From their takeoff point the world looked rather like a pie plate with a slight bulge in the center; the ring was simply a line of light, but it stood out against the background of star-studded blackness and exaggerated the flattening of the giant world.

As power was applied both to kill the moon’s orbital velocity and bring them out of Mesklin’s equatorial plane the picture changed. The ring showed for what it was, but even the fact that it also had two divisions did not make the system resemble that of Saturn. Mesklin’s flattening was far too great for it to resemble anything but itself — a polar diameter of less than twenty thousand miles compared to an equatorial one of some forty-eight thousand has to be seen to be appreciated. All the expedition members had seen it often enough now, but they still found it fascinating.

The fall from the satellite’s orbit gave the rocket a very high velocity, but, as Rosten had said, it was not high enough. Power had to be used in addition; and although the actual pass across the pole was made some thousands of miles above the surface, it was still necessary for the photographer to work rapidly. Three runs were actually made, each taking between two and three minutes for the photography and many more for the whipping journey around the planet. They made reasonably sure that the world was presenting a different face to the sun each time, so that the height of the cliff could be checked by shadow measurements on all sides; then, with the photographs already fixed and on one of the chart tables, the rocket spent more fuel swinging its hyperbola into a wide arc that intercepted Toorey, and killing speed so that too much acceleration would not be needed when they got there. They could afford the extra time consumed by such a maneuver; the mapping could proceed during the journey.

Results, as usual with things Mesklinite, were interesting if somewhat surprising. In diis case, the surprising fact was the size of the fragment of planetary crust that seemed to have been thrust upward en bloc. It was shaped rather like Greenland, some thirty-five hundred miles in length, with the point aimed almost at the sea from which the Bree had come. The river leading to it, however, looped widely around and actually contacted its edge at almost the opposite end, in the middle of the broad end of the wedge. Its height at the edges was incredibly uniform; shadow measurements suggested that it might be a trifle higher at the point end than at the Bree’s present position, but only slightly.

Except at one point. One picture, and one only, showed a blurring of the shadow that might be a gentler slope. It was also in the broad end of the wedge, perhaps eight hundred miles from where the ship now was. Still better, it was upstream — and the river continued to hug the base of the cliff. It looped outward at the point where the shadow break existed as tiiough detouring around the rubble pile of a collapsed slope, which was very promising indeed. It meant diat Barlennan had sixteen or seventeen hundred miles to go instead of fifty, with half of it overland; but even the over-

land part should not be overwhelmingly difficult. Lackland said so, and was answered with the suggestion that he make a more careful analysis of the surface over which his small friend would have to travel. This, however, he put off until after the landing, since there were better facilities at the base.

Once there, microscopes and densitometers in the hands of professional cartographers were a little less encouraging, for the plateau itself seemed rather rough. There was no evidence of rivers or any other specific cause for the break in the wall that Lackland had detected; but the break itself was amply confirmed. The densitometer indicated that the center of the region was lower than the rim, so that it was actually a gigantic shallow bowl; but its depth could not be determined accurately, since there were no distinct shadows across the inner portion. The analysts were quite sure, however, that its deepest part was still well above the terrain beyond the cliffs.

Rosten looked over the final results of the work, and sniffed.

“I’m afraid that’s the best we can do for him,” he said at last. “Personally, I wouldn’t have that country on a bet even if I could live in it. Charlie, you may have to figure out some way to give moral support; I don’t see how anyone can give physical.”

“I’ve been doing my best all along. It’s a nuisance having this crop up when we were so close to home plate. I just hope he doesn’t give us up as a bad job this close to the end; he still doesn’t believe everything we say, you know. I wish someone could explain that high-horizon illusion to his — and my — satisfaction; that might shake him out of the notion that his world is a bowl, and our claim to come from another is at least fifty per cent superstition on our part.”

“You mean you don’t understand why it looks higher?” one of the meteorologists exclaimed in a shocked tone.

“Not in detail, though I realize the air density has something to do with it.”

“But it’s simple enough — ”

“Not for me.”

It’s simple for anyone. You know how the layer of hot air just above a road on a sunny day bends sky light back upward at a slight angle, since the hot air is less dense and the light travels faster in it; you see the sky reflection and tend to interpret it as water. You get more extensive mirages sometimes even on Earth, but they’re all based on the same thing — a ‘lens’ or ‘prism’ of colder or hotter air refracts the light. It’s the same here, except the gravity is responsible; even hydrogen decreases rapidly in density as you go up from Mesklin’s surface. The low temperature helps, of course.”

“All right if you say so; I’m not a — ” Lackland got no chance to finish his remark; Rosten cut in abruptly a and grimly.

“Just how fast does this density drop off with altitude?”

The meteorologist drew a slide rule from his pocket and manipulated it silently for a moment.

“Very roughly, assuming a mean temperature of minus one-sixty, it would drop to about one per cent of its surface density at around fifteen or sixteen hundred feet.” A general stunned silence followed his words.

“And — how far would it have dropped at — say — three hundred feet?” Rosten finally managed to get the question out.

The answer came after a moment of silent lip movement. “Again very roughly, seventy or eighty per cent — probably rather more.”

Rosten drummed his fingers on the table for a minute or two, his eyes following their motions; then he looked around at the other faces. All were looking back at him silently. “I suppose no one can suggest a bright way out of this one; or does someone really hope that Barlennan’s people can live and work under an air pressure that compares to their normal one about as that at forty or fifty thousand feet does to ours?”

“I’m not sure.” Lackland frowned in concentration, and

Rosten brightened a trifle. “There was some reference a long time ago to his staying under water — excuse me, under methane — for quite a while, and swimming considerable distances. You remember those river-dwellers must have moved the Bree by doing just that. If it’s the equivalent of holding breath or a storage system such as our whales use, it won’t do us any good; but if he can actually get a fair part of the hydrogen he needs from what’s in solution in Mesklin’s rivers and seas, there might be some hope.” Rosten thought for a moment longer.

“All right. Get your little friend on the radio and find out all he knows himself about this ability of his. Rick, look up or find out somehow the solubility of hydrogen in methane at eight atmospheres pressure and temperatures between minus one forty-five and one eighty-five Centigrade. Dave, put that slide rule back in your pocket and get to a calculator; get as precise a value of the hydrogen density on that clifftop as physics, chemistry, math, and the gods of good weather men will let you. Incidentally, didn’t you say there was a drop of as much as three atmospheres in the center of some of those tropical hurricanes? Charlie, find out from Barlennan whether and how much he and his men felt that. Let’s go.” The conference broke up, its members scattering to their various tasks. Rosten remained in the screen room with Lackland, listening to his conversation with the Mesklinite far below.

Barlennan agreed that he could swim below the surface for long periods without trouble; but he had no idea how he did it. He did not breathe anyway, and did not experience any feeling comparable to the human sense of strangulation when he submerged. If he stayed too long and was too active the effect was rather similar to sleepiness, as nearly as he could describe it; if he actually lost consciousness, however, it stopped there; he could be pulled out and revived as much later as anyone cared as long as he didn’t starve in the meantime. Evidently there was enough hydrogen in solution in Mesklin’s seas to keep him alive, but not for normal activity. Rosten brightened visibly.

“There is no discomfort of the sort you suggest in the middle of the worst storms I have ever experienced,” the captain went on. “Certainly no one was too weak to hold on during that one which cast us on the island of the gliders — though we were in its center for only two or three minutes, of course. What is your trouble? I do not understand what all these questions are leading to.” Lackland looked to his chief for permission, and received a silent nod of affirmation.

“We have found that the air on top of this cliff, where our rocket is standing, is very much thinner than at the bottom. We doubt seriously that it will be dense enough to keep you and your people going.”

“But that is only three hundred feet; why should it change that much in such a short distance?”

“It’s that gravity of yours; I’m afraid it would take too long to explain why, but on any world the air gets thinner as you go higher, and the more the gravity the faster that change. On your world the conditions are a trifle extreme.”

“But where is the air at what you would call normal for this world?”

“We assume at sea level; all our measures are usually made from that reference.”

Barlennan was thoughtful for a little while. “That seems silly; I should think you’d want a level that stayed put to measure from. Our seas go up and down hundreds of feet each year — and I’ve never noticed any particular change in the air.”

“I don’t suppose you would, for several reasons; the principal one is that you would be at sea level as long as you were aboard the Bree, and therefore at the bottom of the atmosphere in any case. Perhaps it would help you to think of this as a question of what weight of air is above you and what weight below.”

“Then there is still a catch,” the captain replied. “Our cities do not follow the seas down; they are usually on the seacoast in spring and anywhere from two hundred miles to two thousand inland by fall. The slope of the land is very gentle, of course, but I am sure they are fully three hundred feet above sea level at that time.” Lackland and Rosten stared silently at each other for a moment; then the latter spoke. “But you’re a lot farther from — the pole in your country — but no, that’s quibbling. Even if gravity were only a third as great you’d be experiencing tremendous pressure changes. Maybe we’ve been taking nova precautions for a red dwarf.” He paused for a moment, but the Mesklinite made no answer. “Would you be willing, then, Barlennan, to make at least an attempt to get up to the plateau? We certainly will not insist on your going on if it proves too hard on your physical make-up, but you already know its importance to us.” “Of course I will; we’ve come this far, and have no real reason to suppose what’s coming will be any worse than what’s past. Also, I want…” He paused briefly, and went on in another vein. “Have you yet found any way of getting up there, or is your question still hypothetical?” Lackland resumed the human end of the conversation.

“We have found what looks like a way, about eight hundred miles upstream from your present position. We can’t be sure you can climb it; it resembles a rock fall of very moderate slope, but we can’t tell from our distance how big the rocks may be. If you can’t get up there, though, I’m afraid you just can’t get up at all. The cliff seems to be vertical all around the plateau except for that one point.”

“Very well, we will head upstream. I don’t like the idea of climbing even small rocks here, but well do our best. Perhaps you will be able to give suggestions when you can see the way through the vision sets.”

“It will take you a long time to get there, I’m afraid.” “Not too long; for some reason there is a wind along the cliff in the direction we wish to go. It has not changed in direction or strength since we arrived several score days ago. It is not as strong as the usual sea wind, but it will certainly pull the Bree against the current — if the river does not grow too much swifter.”

“This one does not grow too much narrower, at any rate, as far as you will be going. If it speeds up, it must be because it grows shallower. All we can say to that is that (there was no sign of rapids on any of the pictures.”

“Very well, Charles. We will start when the hunting parties are all in.”

One by one the parties came back to the ship, all with some food but none with anything interesting to report. The rolling country extended as far iri all directions as anyone had gone; animals were small, streams scarce, and vegetation sparse except around the few springy. Morale was a trifle low, but it improved with the news that the Bree was about to travel again. The few articles of equipment that had been disembarked were quickly reloaded on the rafts, and the ship pushed out into the stream. For a moment she drifted seaward, while the sails were being set; then they filled with the strangely steady wind and she bore up against the current, forging slowly but steadily into unknown areas of the hugest planet man had yet attempted to explore.