The Book of All Skies, page 19
“You’ve really lit a fire,” Imogen marveled. “You just muttered a few words, but by the time this is finished, they’ll be able to tell us how to build a new bridge out of paper alone.”
“Ha.” There was enough of it on the table to make a start. “Maybe the world really should be split in two for a few generations at a time, then brought back together so we can reinvigorate each other with the things one side discovered but the other missed.”
Del picked up a sudden note of excitement in Sina’s voice, and listened carefully as she addressed Asha. “The total potential from the charge – if you add it up across equivalent points in all the different skies – is still just proportional to the inverse distance. That has to be true, or there’d be lines of flux disappearing for no reason. But this formula tells us how to split up the total into separate parts, each of them obeying the same equation that the inverse distance obeys on its own. And that’s it. That’s enough to be sure that the solution is correct!”
Asha gazed down at the scrawled symbols. Then she looked up and smiled. “You’re right. I understand now.”
“So you can calculate the gravity?” Del asked hopefully.
“For one speck of rock,” Asha replied. “Now we need to add up the results for all the specks that make up the world.”
Imogen laughed. Del believed that Montano and Silvio had done something similar; there were mathematical techniques to make this less like emptying an ocean with a spoon than it sounded. But it wouldn’t be easy.
Del offered to cook some food for the group, and after some initial, polite refusals the balloonists agreed. Imogen joined her in the kitchen, grumbling. “We’re not their servants.”
“And they’re not ours,” Del replied, “but we’re asking them to risk their lives. Gutting a few fish and chopping a few vegetables is hardly servitude – it’s what they did for us last time we were here.”
When the meal was ready they brought it into the dining room, and everyone took a break.
“Any progress?” Del asked.
“We have some estimates,” Asha said cautiously.
“And are they good news, or bad?”
Asha glanced at her sister. “The problem is, if the strength of gravity changes too rapidly with a change in altitude, anything that disturbs the overall buoyancy of the airship could make it drop much faster than usual. It takes time to react to an event like that, and compensate for it. We’re accustomed to dealing with changes in the temperature and pressure of the air, and with up-drafts and down-drafts over land and water; we know how strong these effects are, and we’re confident we can adjust the buoyancy quickly enough to deal with them. But if gravity can double between the time we start to plummet and the time we’ve responded to the fall ... ”
“Can it double that fast, though?” Imogen asked.
“That depends,” Asha replied.
“On what?”
“How accurate our estimates are. But also, on how high we fly.”
“The higher you fly,” Del guessed, “the gentler the changes in gravity?”
“Yes,” Asha confirmed.
Imogen chewed on her fish for a while, but Del could see that she was mulling over the problem. “What is it that limits the altitude you can reach?” she asked finally. “The buoyancy you can get from the balloon, or something else?”
Lena said, “Something else. Unpiloted balloons can ascend much higher than piloted ones, but engines and pilots both need to breathe. We could swap the fuel-based engines for electric ones, for a short enough trip, but people aren’t so easy to adapt.”
Imogen said, “You store hydrogen gas in a metal cylinder. Is there any reason you couldn’t do the same with breathable air?”
“Not in principle,” Lena replied. “But something like that would be completely new and untried. It might be possible to work out a safe way to deliver that air to a person, but I wouldn’t know where to start.”
Del waited for Imogen to respond, but she was pretending to concentrate on her meal, mopping up the gravy as if she had nothing more to contribute.
Del ran out of patience and turned to Asha. “Have you ever walked underwater?” she asked. “Because my friend has a lot of experience with the machinery that makes that possible.”
Chapter 32
Del leaned over the edge of the basket and gazed down at the cloud-strewn landscape below. In between the fluffy gray streaks, she could see the lake catching the starlight, and the dark fields to the north. On the southern shore, the streets of Medoun had shrunk to a patch of luminous tracery she could cover with one hand. Her faceplate was still fogging up from the cold; they would need to do something about that.
When she looked up, she was confused for a moment; her eye-line felt perfectly level, but the horizon lay well below it. Then she realized that that made perfect sense: this high above the ground, even Dallya’s entire globe would fill less than half the sky.
“Are you ready?” Katka asked. Her voice sounded thin through the rarefied air.
Del wasn’t ready for anything at this altitude besides a mug of Imogen’s special tea, but it was her turn to face the terror. If she wasn’t willing to do this, she should have stayed on the ground. “Yes,” she replied.
Katka plunged a knife into the bag of sand attached to the side of the basket, then carved out a larger wound, like an assassin making sure of her kill. As sand trickled out the balloon began to rise, sending Del’s viscera twitching and shuddering. She grabbed the handle of the pump and began working it frantically, forcing air into the ballonet.
The instrument panel showed the ambient pressure, the pressure in the hydrogen-filled lifting capsule, and the pressure in the ballonets. The first was still dropping – a surer judge of rising altitude than her gut – so Del redoubled her efforts. In a real emergency where the ballonet pump’s electric motor failed, she hoped there’d be at least one other pair of hands to assist her, but the balloonists were adamant that every pilot and passenger had to be prepared to stabilize the airship’s altitude, unaided, if the need arose.
Finally, the first dial became steady. Del looked over at the sandbag, but it was empty; there was no more ballast to lose.
“Did I really pump in the same weight in air as you dropped in sand?” she asked.
“Not yet,” Katka replied. “We’re higher now, so that’s shifted the balance. You need to go further, and bring us down to where we were before.”
Del resumed pumping, then realized she was near the limits of both her own ability to move the handle and the physical capacity of the first ballonet. She shifted to the second pump; it was still hard work, pushing air in to squeeze against the hydrogen she’d already compressed.
Suddenly, their altitude began dropping. Del stopped pumping, but the descent continued.
“What’s happening?” she asked, bewildered. “What did I do?”
“Look at the dials,” Katka urged her.
Del stared at the panel, trying not to panic. The hydrogen pressure had dropped. “You vented it?” she asked Katka. “Without warning?”
“Events don’t always come with warnings.”
Del opened the vents on both ballonets; as the air escaped, the hydrogen pressure dropped further, but this time it wasn’t being lost. Or so she hoped. She checked the lever on the hydrogen vent, but Katka had closed it after her surreptitious intervention, and she hadn’t accidentally opened it herself.
She watched the three needles moving, her stomach convulsing. But gradually the altitude leveled, and she quickly shut off the ballonet vents.
She glanced down and saw Medoun revealed as a city again, the carts moving about like delicate toys. Katka said, “Between the nubs, the scale of things will be compressed. The highest altitude we can survive, and the lowest, will be ten times closer than they are here.”
Del’s hands were shaking as she removed her helmet. “But you think we can survive the crossing?”
“Absolutely,” Katka replied. “I wouldn’t try doing it if I thought otherwise. But could it kill us, if enough things go wrong? Of course. We just need to make the quantity of bad luck needed to achieve that as large as we possibly can.”
Del wasn’t sure how comforted she should feel. “Every time you race your cousins, one of you could die. Maybe you’re more used to that than I am.”
“You almost died once, coming here,” Katka observed. “But you didn’t.”
“Twice,” Del corrected her.
“Twice?”
She had no choice, now, but to recount the ambush in Zeruma.
Katka was horrified. “That’s how people treat each other, on your side of the gap? They kill each other for gold?”
Del laughed. “Not most people. It’s not ... generally approved.” She didn’t know how to say “unlawful.”
Katka took over the airship’s controls; when she started the electric motor, its gentle whir barely rose above the sound of the wind. “Why do you think your people blocked off the tunnel?” she asked Del.
“I don’t know. I don’t think of them as ‘my people’; it was so long ago, and if they ever explained themselves, whatever they wrote on the subject has been lost. I’m not even sure if any of the commentary I’ve read about the route to the Bounteous Lands was a genuine debate, or if it was all disinformation, deliberately sown to confuse people.”
Katka was bewildered. “Why would anyone do that?”
Del said, “For the same reason they blocked the tunnel.”
“Why not just state their reasons for blocking it? If they could make a good enough argument for that, no one would want to dig through.”
Del had been turning that question over in her mind ever since her meeting with Grana. “It only makes sense if the thing they were most afraid of from your side was an idea. If you believe an idea is dangerous, you can’t warn people off it by explaining it to them, since all you’ll end up doing is planting it in their head.”
They were close to the tower now. Katka threw out the anchor rope and managed to hook a girder, then Lena, who’d been waiting for them in the tower, stepped forward and secured the connection before sliding out the crossing ladder.
Del went first, in the hope that her fear of Katka’s impatience would prevent her from freezing halfway. Staring down at the shore with just the rungs between her and a long drop made her heart race, but the trick seemed to work. The tower itself was all open girders and platforms: no more frightening than the bridge, and much less likely to collapse unexpectedly.
“How did it go?” Lena asked her.
“I’m not sure,” Del admitted. “We survived the test, but I don’t know if we would have survived the same kind of event in the gap.”
Katka joined them on the platform. “We were close,” she said. “We just need some improvements to the pumps, and some more practice to reduce our reaction times.”
Del said, “I don’t know if this is practical or not, but is there any way to show the volume of the ballonet on the instrument panel, as well as the pressure inside it?”
Lena was puzzled. “Why would you want that?”
“It would give me a clearer picture of what’s going on,” Del replied. The pressures were crucial, but they were abstract numbers to her; she wanted the means to visualize as much as she could about the changes in any structure on which her life would depend.
“I’ll think about it,” Lena said. “Maybe there’s a simple way to do it without adding another failure point.”
Back at the house, Asha and Sina were working on yet another refinement of their gravitational calculations. Del stared at the charts on the wall, which looked like topographical maps but actually portrayed empty space. The curves of constant potential progressed from lines radiating out from the edge of the Hoop, to spirals, to circles, then back again, which was in accord with her own experience on the bridge.
“If you can get everything that I know about right, how much room is there to be wrong about the rest?” she asked Asha.
Asha hesitated, but Sina answered. “Not a lot, unless we’ve made an arithmetical error somewhere. It’s in the nature of the gravitational force that if you know how it behaves on the boundary of a region, you know how it behaves in the interior.”
Asha was a little more circumspect. “That’s true for an entire boundary, but we only know what things were like along one path. We can push it a bit further by assuming there was nothing special about that path – but in the end, nothing’s certain until you’ve measured it.”
Del recalled Clarissa’s hope that successive measurements as the bridge grew would alert her to any failure in the calculations. But she still didn’t know if it was the calculations that had failed them in the end.
Imogen and Sejan joined them, back from the food stall, and they all sat down for a meal.
“I’ve been thinking about the trip to the nub,” Lena began. “If we take the airships apart and move them by cart, that would be faster, and less subject to the vagaries of the wind, but it won’t give us much of a chance to test them after reassembly. If we fly them the whole way, we’ll get to see them under stress while we still have ground to land on if we need to carry out repairs.”
“That makes sense to me,” Katka replied.
Sejan said, “I was hoping to get in some observations on the way back.”
“You can still do that,” Lena assured him. “If you’re driving the cart, and we’re following along by air, there’ll be plenty of time for you to stop and use the telescopes while you wait for us to catch up.”
“We would need to leave earlier, though,” Asha said. She turned to Sina. “Are you sure you don’t want to come with us?”
Sina laughed. “I can just about cope with an ordinary flight, but losing sight of the ground completely is my idea of a nightmare.” She addressed Del and Imogen. “Seriously, when that bridge had no visible means of support, how did you keep going?”
“With one foot in front of the other,” Del replied. “Thankful that I wasn’t a carpenter.”
“How soon until we’d need to leave?” Imogen asked Asha.
“About thirty days.”
Sejan pondered this. “Twenty might be better.”
Katka said, “That should work.”
Del’s chest tightened. “How many more test flights will Imogen and I have time for?”
“Maybe ... half a dozen each,” Lena suggested.
“And you think we’ll be ready?” Del felt like she was watching sand pouring out of a ballast sack again.
“You’ll have the chance to observe all the operations on a much longer flight along the way,” Katka replied. “By the time we reach the nub, you’ll be experienced copilots.”
Imogen exchanged a glance with Del. “How many lands have the three of you flown between, so far?”
The balloonists went quiet, but then Lena said, “We’ve all been through the Hoop and back once, just to convince ourselves that it was possible. We never had reason to travel very far before. But as I said, the more we have a chance to test the airships before the crossing, the better.”
Del helped wash the dishes, then she went for a walk. The household wasn’t short on any provisions, but out of habit she ended up wandering past the stalls in the town center where people left things they’d made, or obtained, for others to take as they wished. Most stalls were unattended by the providers of the goods, but there were always a few touts to be seen, so passionate about their creations that they harangued passersby with a constant monolog on the virtues of the product. “This mop will clean twice as thoroughly as any other design!” a man exclaimed, holding up the glorious device. “And if the head becomes worn or dirty, it’s easily replaced!”
When Del came to the bookstall, there was no one speaking on behalf of the wares. She had borrowed a few volumes since arriving in town – an eclectic mix of titles she’d chanced upon, chosen mainly on the basis that the first half-page had been comprehensible to her, despite her limited grasp of the language.
She entered and switched on the light, then walked between the shelves, waiting for something to catch her eye. The Murderer’s Apprentice and its seventeen sequels occupied a substantial portion of the stall; Del had tried the first volume, and found it quite entertaining, but she’d lost interest by the fifth killing. For a largely peaceful society with almost no concept of property crimes, the Overgaps still managed to maintain a lurid obsession with violence to rival anything from the Vitean age.
She spotted a new title on the maintenance of engines, and took it in case it was of interest to Imogen. She turned and headed back toward the exit, then paused; for a moment she wasn’t sure why.
The Book of All Skies sat on a shelf beside her, the cover crisply printed with a simple illustration portraying a helicoid decorated with star maps. Del picked it up; the binding was uncreased, and it looked as if no one had opened the volume before her.
Sejan had always claimed that the book was widely available, but when she’d failed to locate it in her previous visits to the stall she’d started to wonder if that merely reflected his own experience in another land. But she wasn’t hallucinating, or mistranslating the title; the words in front of her were exactly the words he’d used.
She opened the book and began to read.
Long ago, our ancestors lived on Old Jierra, a world with an uncomplicated, spherical shape from which every land we now live upon was formed.
Chapter 33
Given that the expedition would be robbing Medoun of its heroes for at least a year, Del had expected to find the crowd gathered at the shore for their departure hostile, mournful, or perhaps just entirely absent.
But when she arrived, the site was as packed as she’d ever seen it, and the people every bit as exuberant.
“Why do they love you so much?” she asked Katka, as they approached the tower. People were running in front of the cart, waving at them blissfully, as ecstatic as if some despotic ruler had just dropped dead.
