"Ah. I see." She did not mind. They had long forgotten the relationship of Captain and crew. She laughed, and shook her head. "All right. What's your plan?"
"First look around. Later-four or five years from now-we'd look pretty foolish if me of the builders asked why we didn't use the elevator."
CHAPTER TWENTY-ONE
It was roughly 250 kilometers around the base of the spoke. They began to circumnavigate it, looking for anything from a rope ladder to an anti-gravity helicopter. What they found was horizontal trees, growing in the vertical forest.
When they penetrated the outer branches and followed the trunks to their roots in the wall, they had to climb a gradual slope made of fallen branches and rotting leaves. The real sub- stance of the spoke was a spongy gray material. It yielded like soft rubber when they pressed it. When Cirocco pulled a bush from the wall, a long taproot came out with it. The wall bled a thick, milky fluid, then closed around the small hole.
There was no soil, and very little sun; bright as it had seemed when they came out of the dark staircase, the real light level was quite low. Cirocco assumed that, like many of the plants on the rim, these depended m sub-surface sources for life.
The wall itself was moist and supported growths of moss and lichen, but few intermediate-sized plants. There were no grasses, and what vines existed were parasitic, rooting in the tree trunks. Many of the trees were the same species they had seen on the rim, adapted for a horizontal existence. There were familiar fruits and nuts growing on them.
"That takes care of the food problem," Gaby said.
There could be no rivers in the spoke, but the wall glistened with tiny trickles. High above, sports could be seen, arching out and turning to mist long before they reached the floor.
Gaby looked up at them, noting that they seemed evenly distributed, like lawn sprinklers.
"So much for dying of thirst."
It began to seem that the climb would not actually be impossible. Cirocco found it hard to be elated about it.
Excluding the possibility of a staircase-which she quickly concluded they would not find, since the trees prevented a close exploration of the wall-there were two ways to the top.
One involved climbing the trees themselves. it should be possible, Cirocco reckoned, to go from branch to branch out where spreading had meshed the branches of one tree with those of its neighbors.
The other possibility was a straightforward job of mountaineering. They found that their metal spikes could be driven into the wall surface simply by holding them and jabbing.
Cirocco favored the wall, not wanting to trust the trees. Gaby liked the branches, which would be quicker. They debated it until the second day, when two things happened.
Gaby noticed the first thing while looking ~ over the gray floor of the spoke. Her eyes narrowed, and she pointed.
"I think that hole's not there anymore," she said. Cirocco squinted, but could not be sure. "Let's climb up and take a look."
They roped themselves together and began ascending through the branches.
It was not as bad as Cirocco had feared. Like anything else, there was an optimum way to go about it, and they quickly discovered what it was. There was a line to pick between the thicker branches closer to the wall-which were rock solid, but tended to be too far apart-and the thinner, more willowy ones farther out, which provided a thousand places for hands and feet but sagged under their weight. .
"A little farther in," Cirocco called ahead to Gaby, who had taken the job of scouting the path at the end of a five-meter tether. "I'd say about two-thirds of the way to the top of the tree is about right."
"In, top," Gaby said. "You're mi2dng your directions."
"The bottoms of the trees are in close to the wall. The tops are out in the air. What could be simpler?"
"Suits me."
After climbing through ten trees they began to work their way out to the top of the last one.
When the branches they walked on began to bend, they tied a line to a strong me. Now the sag worked to their advantage, as it opened a window in an otherwise impenetrable wall of foliage. They had chosen a tree that, in a horizontal forest, would have towered above its neighbors. In the spoke it had to be content with jutting further from the wall.
"You were right. It's gone."
"No I wasn't. But it will be in a minute."
Cirocco saw what was left of the hole. It was a tiny black oval in the gray floor, and she could see it contracting like the iris of an eye. From below, the only time they had a good lock at it, that hole had been nearly as large as the spoke itself. Now it was less than ten kilometers across, and still closing. Soon it would seal around the vertical cables that emerged from its center.
"Any ideas?" Gaby asked. "Mat good does it do to close the spoke off from the rim?"
"I haven't the faintest idea. I presume it will open again, though, The angels got through it, they come through regularly, so it..." She paused, and then smiled.
"It's the breath of Gaea."
"Say again?"
"It's what the Titaffides call the wind from the east. Oceanus brings cold weather and the Lament, and Rhea brings hot air and the angels. So you've got a tube 300 kilometers high, with a valve on each end. You could use it as a pump. You could create high and low pressure areas, and use them to move air."
"How would you go about that?" Gaby asked.
"I can think of two ways. Some kind of moveable piston to compress or rarefy the air. I don't see one, and I sure as hell hope there isn't or it'd smear us."
"If there was, it wouldn't have done these trees any good."
"Right. so it's the other method. The walls can expand or contract. Close the bottom valve and open the top one, expand the spoke, and you draw air in from the top. Close the top and open the bottom, put on the big squeeze, and you force it out over the rim."
"Where does the air that comes in the top come from?"
"It's either sucked up through the cables-some of it must be, we saw that-or it comes from the other spokes. They all connect at the top. With a few more valves, you can use the spokes against each other. Open and close a few, and you end up sucking air out of Oceanus, through the hub, and into this spoke. Then open and close some more, and force it down over Rhea. Now if I only knew why the builders thought it was necessary."
Gaby looked thoughtful. "I think I can give you that. It's something that's bothered me. Why doesn't all the air pool at the botton down at the rim? The air's thinner up here, but it's still okay because the air pressure at the rim is higher than Earth-normal. And in low gravity, pressure sure drops off less quickly. Mars' atmosphere isn't much, for instance, but it goes out a long way. Then if you keep the air circulating, it doesn't have time to settle. You can keep adequate air pressure all the way through Gaea."
Cirocco nodded, then sighed. "All right. You've just disposed of the last objection to the climb. We've got food and water, or at least it looks like we will. Now it looks like we'll have air, too. What do you say we get going? "
"How about exploring the rest of the wall?"
"Mat's the use? We might already have passed what we're looking for. There's just no way to see it."
"I guess you're right. Okay, lead on."
The climbing was hard work, tedious, and yet requiring full attention. They got better at it -as they went along, but Cirocco knew it would never get as easy as the climb up the cable.
The one consolation at the end of the first ten-hour climb was that they were in shape. Cirocco was weary and there was a blister on her left palm, but aside from a slight backache she felt all right. It would be good to sleep. They climbed out to the top of a tree for a look down before making camp.
"Will your system measure a height like that?" Gaby frowned, and shook her head.
"Not well." She held her hands out, made a square with them, and squinted. "I'd say-yeow! "
Cirocco grabbed her under one arm, steadying herself by holding a branch over her head.
"Thanks. What a fall that would have been."
"You had your rope," Cirocco pointed out.
"Yeah, but I don't really want to swing on the end of it." She caught her breath, then looked at the ground again.