up the final stretch silently. Denison was aware of the smoother area to their side; a wide swathe of slope from which most of the dust had been brushed.
“That’s too smooth for a beginner to work up,” Selene said, answering his thoughts. “Don’t get too ambitious or you’ll want me to teach you the kangaroo-hop next.”
She made a kangaroo-hop as she spoke, turned about face almost before landing, and said, “Right here. Sit down and I’ll adjust—”
Denison did, facing downhill. He looked down the slope uncertainly. “Can you really glide on it?”
“Of course. The gravity is weaker on the Moon than on the Earth, so you press against the ground much less strongly, and that means there is much less friction. Everything is more slippery on the Moon than on the Earth. That’s why the floors in our corridors and apartments seemed unfinished to you. Would you like to hear me give my little lecture on the subject? The one I give the tourists?”
“No, Selene.”
“Besides, we’re going to use gliders, of course.” She had a small cartridge in her hand. Clamps and a pair of thin tubes were attached to it.
“What is that?” asked Ben.
“Just a small liquid-gas reservoir. It will emit a jet of vapor just under your boots. The thin gas layer between boots and ground will reduce friction to virtually zero. You’ll move as though you were in clear space.”
Denison said uneasily. “I disapprove. Surely, it’s wasteful to use gas in this fashion on the Moon.”
“Oh, now. What gas do you think we use in these gliders? Carbon dioxide? Oxygen? This is waste gas to begin with. It’s argon. It comes out of the Moon’s soil in ton-lots, formed by the billions of years of breakdown of potassium-40.… That’s part of my lecture, too, Ben.… The argon has only a few specialized uses on the Moon. We could use it for gliding for a million years without exhausting the supply.… All right. Your gliders are on. Now wait till I put mine on.”
“How do they work?”
“It’s quite automatic. You just start sliding and that will trip the contact and start the vapor. You’ve only got a few minutes supply; but that’s all you’ll need.”
She stood up and helped him to his feet. “Face downhill.… Come on, Ben, this is a gentle slope. Look at it. It looks perfectly level.”
“No, it doesn’t,” said Denison, sulkily. “It looks like a cliff to me.”
“Nonsense. Now listen to me and remember what I told you. Keep your feet about six inches apart and one just a few inches ahead of the other. It doesn’t matter which one is ahead. Keep your knees bent. Don’t lean into the wind because there isn’t any. Don’t try to look up or back, but you can look from side to side if you have to. Most of all, when you finally hit level, don’t try to stop too soon; you’ll be going faster than you think. Just let the glider expire and then friction will bring you to a slow halt.”
“I’ll never remember all that.”
“Yes, you will. And I’ll be right at your side to help. And if you do fall and I don’t catch you, don’t try to do anything. Just relax and let yourself tumble or slide. There are no boulders anywhere that you can collide with.”
Denison swallowed and looked ahead. The southward slide was gleaming in Earthlight. Minute unevennesses caught more than their share of light, leaving tiny uphill patches in darkness so that there was a vague mottling of the surface. The bulging half-circle of Earth rode the black sky almost directly ahead.
“Ready?” said Selene. Her gauntleted hand was between his shoulders.
“Ready,” said Denison faintly.
“Then off you go,” she said. She pushed and Denison felt himself begin to move. He moved quite slowly at first. He turned toward her, wobbling, and she said, “Don’t worry. I’m right at your side.”
He could feel the ground beneath his feet—and then he couldn’t. The glider had been activated.
For a moment he felt as though he were standing still. There was no push of air against his body, no feel of anything sliding past his feet. But when he turned toward Selene again, he noticed that the lights and shadows to one side were moving backward at a slowly increasing speed.
“Keep your eyes on the Earth,” Selene’s voice said in his ear, “till you build up speed. The faster you go, the more stable you’ll be. Keep your knees bent.… You’re doing very well, Ben.”
“For