Hal Clement - Heavy Planet

“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 percent 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 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 percent 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 percent — 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 cliff top 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.”