Selene sat facing him, at right angles'. He could see her face now and then, dimly through the faceplate, when the Earthlight caught it at the proper angle.

She said, "Don't you see the stars on Earth?"

"Not like this. Even when there are no clouds, the air on Earth absorbs some of the light. Temperature differences in the atmosphere make them twinkle, and city lights, even distant city lights, wash them out"

"Sounds disgusting."

"Do you like it out here, Selene? On the surface?"

"I'm not crazy about it really, but I don't mind it too much, now and then. It's part of my job to bring tourists out here, of course."

"And now you have to do it for me."

"Can't I convince you it's not the same thing at all, Ben? We've got a set route for the tourists. It's very tame, very uninteresting. You don't think we'd take them out here to the slide, do you? This is for Lunarites - and Immies. Mostly Immies, actually."

"It can't be very popular. There's no one here but ourselves."

"Oh, well. There are particular days for this sort of thing. You should see this place on race days. You wouldn't like it then, though."

"I'm not sure I like it now. Is gliding a sport for Immies, particularly?"

"Rather. Lunarites don't like the surface generally."

"How about Dr. Neville?"

"You mean, how he feels about the surface?"

"Yes."

"Frankly, I don't think he's ever been up here. He's a real city boy. Why do you ask?"

"Well, when I asked permission to go along on the routine servicing of the Solar batteries, he was perfectly willing to have me go, but he wouldn't go himself. I rather asked him to, I think, so I could have someone answer my questions, if there were any, and his refusal was rather strong."

"I hope there was someone else to answer your questions."

"Oh, yes. He was an Immie, too, come to think of it. Maybe that explains Dr. Neville's attitude toward the Electron Pump."

"What do you mean?"

"Well - " Denison leaned back and kicked his legs up alternately, watching them rise and fall slowly with a certain lazy pleasure. "Hey, that's not bad. Look, Selene -  What I mean is that Neville is so intent on developing a Pump Station on the Moon when the Solar batteries are so adequate for the job. We couldn't use Solar batteries on the Earth, where the Sun is never as unfailing, as prolonged, as bright, as radiant in all wave lengths. There's not a single planetary body in the Solar system, no body of any size, that is more suitable for the use of the batteries than the Moon is. Even Mercury is too hot. - But the use does tie you to the surface, and if you don't like the surface - "

Selene rose to her feet suddenly, and said, "All right, Ben, you've rested enough. Up! Up!"

He struggled to his feet and said, "A Pump Station, however, would mean that no Lunarite would ever have to come out on the surface, if he didn't want to."

"Uphill we go, Ben. Well go to that ridge up ahead. See it, where the Earthlight cuts off in a horizontal line?"

They made their way 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 unevenness 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 an Immie," gasped Denison. "How does it feel?"

"Like flying," he said. The pattern of light and dark on either side was moving backward in a blur. He looked briefly to one side, then the other, trying to convert the sensation of a backward flight of the surroundings into one of a forward flight of his own. Then, as soon as he succeeded, he found he had to look forward hastily at the Earth to regain his sense of balance. "I suppose that's not a good comparison to use to you. You have no experience of flying on the Moon."

"Now I know, though. Flying must be like gliding - I know what that is."

She was keeping up with him easily.

Denison was going fast enough now so that he got the sensation of motion even when he looked ahead. The Moonscape ahead was opening before him and flowing past on either side. He said, "How fast do you get to go in a glide?"

"A good Moon-race," said Selene, "has been clocked at speeds in excess of a hundred miles an hour - on steeper slopes than this one, of course. You'll probably reach a top of thirty-five."

"It feels a lot faster than that somehow."

"Well, it isn't. We're leveling off now, Ben, and you haven't fallen. Now just hang on; the glider will die off and you'll feel friction. Don't do anything to help it. Just keep going."

Selene had barely completed her remarks when Denison felt the beginning of pressure under his boots. There was at once an overwhelming sensation of speed and he clenched his fists hard to keep from throwing his arms up in an almost reflex gesture against the collision that wasn't going to happen. He knew that if he threw up his arms, he would go over backward.

He narrowed his eyes, held his breath till he thought his lungs would explode, and then Selene said, "Perfect, Ben, perfect. I've never known an Immie to go through his first slide without a fall, so if you do fall, there'll be nothing wrong. No disgrace."

"I don't intend to fall," whispered Denison. He caught a large, ragged breath, and opened his eyes wide. The Earth was as serene as ever, as uncaring. He was moving more slowly now - more slowly - more slowly -

"Am I standing still now, Selene?" he asked. "I'm not sure."

"You're standing still. Now don't move. You've got to rest before we make the trip back to town. . . . Damn it, I left it somewhere around here when we came up."

Denison watched her with disbelief. She had climbed up with him, had glided down with him. Yet he was half-dead with weariness and tension, and she was in the air with long kangaroo-leaps. She seemed a hundred yards away when she said, "Here it is!" and her voice was as loud in his ears as when she was next to him.

She was back in a moment, with a folded, paunchy sheet of plastic under her arm.

"Remember," she said, cheerily, "when you asked what it was on our way up and I said we'd be using it before we came down?" She unfolded it and spread it on the dusty surface of the Moon,

"A Lunar Lounge is its full name," she said, "but we just call it a lounge. We take the adjective for granted here on this world." She inserted a cartridge and tripped a lever.

It began to fill. Somehow Denison had expected a hissing noise, but of course there was no air to carry sound.

"Before you question our conservation policies again," said Selene, "this is argon also."

It blossomed into a mattress on six, stubby legs, "It will hold you," she said. "It makes very little actual contact with the ground and the vacuum all around will conserve its heat."

"Don't tell me it's hot," said Denison, amazed.

"The argon is heated as it pours in, but only relatively. It ends up at 270 degrees absolute, almost warm enough to melt ice, and quite warm enough to keep your insulated suit from losing heat faster than you can manufacture it. Go ahead. Lie down."

Denison did so, with a sensation of enormous luxury.

"Great!" he said with a long sigh.

"Mamma Selene thinks of everything," she said.

She came from behind him now, gliding around him, her feet placed heel to heel as though she were on skates, and then let them fly out from under her, as she came down gracefully on hip and elbow on the ground just beside him.

Denison whistled. "How did you do that?"

"Lots of practice! And don't you try it. You'll break your elbow. I warn you though. If I get too cold, I'm going to have to crowd you on the lounge."

"Safe enough," he said, "with both of us in suits."

"Ah, there speaks my brave lecher . . . How do you feel?"

"All right, I guess. What an experience!"

"What an experience? You set a record for non-falls. Do you mind if I tell the folks back in town about this?"

"No. Always like to be appreciated . . . You're not going to expect me to do this again, are you?"

"Right now? Of course not I wouldn't myself. Well just rest awhile, make sure your heart action is back to normal, and then we'll go back. If you'll reach your legs in my direction, I'll take your gliders off. Next time, I'll show you how to handle the gliders yourself."

"I'm not sure that there will be a next time."

"Of course there'll be. Didn't you enjoy it?"

"A little. In between terror."

"You'll have less terror next time, and still less the time after, and eventually you'll just experience the enjoyment and I'll make a racer out of you."

"No, you won't. I'm too old."

"Not on the Moon. You just look old."

Denison could feel the ultimate quiet of the Moon soaking into him as he lay there. He was facing the Earth this time. Its steady presence in the sky had, more than anything else, given him the sensation of stability during his recent glide and he felt grateful to it.

He said, "Do you often come out here, Selene? I mean, by yourself, or just one or two others? You know, when it isn't fiesta time?"

"Practically never. Unless there are people around, this is too much for me. That I'm doing it now, actually, surprises me."

"Uh-huh," said Denison, noncommittally.

"You're not surprised?"

"Should I be? My feeling is that each person does what he does either because he wants to or he must and in either case that's his business, not mine."

"Thanks, Ben. I mean it; it's good to hear. One of the nice things about you, Ben, is that for an Immie, you're willing to let us be ourselves. We're underground people, we Lunarites, cave people, corridor people. And what's wrong with that?"

"Nothing."

"Not to hear the Earthies talk. And I'm a tourist guide and have to listen to them. There isn't anything they say that I haven't heard a million times, but what I hear most of all" - and she dropped into the clipped accents of the typical Earthie speaking Planetary Standard " - 'But, dear, however can all you people live in caves all the time? Doesn't it give you a terrible closed-in feeling? Don't you ever want to see blue sky and trees and ocean and feel wind and smell flowers - '

"Oh, I could go on and on, Ben. Then they say, 'But I suppose you don't know what blue sky and sea and trees are like so you don't miss them.' . . . As if we don't receive Earth-television and as if we don't have full access to Earth-literature, both optical and auditory - and olfactory sometimes, too."

Denison was amused. He said, "What's the official answer to remarks like that?"

"Nothing much. We just say, 'We're quite used to it, madam.' Or 'sir' if it's a man. Usually it's a woman. The men are too interested in studying our blouses and wondering when we take them off, I suppose. You know what I'd like to tell the idiots?"

"Please tell me. As long as you have to keep the blouse on, it being inside the suit, at least get that off your chest"

"Funny, funny word play! . . . I'd like to tell them, 'Look, madam, why the hell should we be interested in your damned world? We don't want to be hanging on the outside of any planet and waiting to fall off or get blown off. We don't want raw air puffing at us and dirty water falling on us. We don't want your damned germs and your smelly grass and your dull blue sky and your dull white clouds. We can see Earth in our own sky when we want to, and we don't often want to. The Moon is our home and it's what we make it; exactly what we make it. We own it and we build our own ecology, and we don't need you here being sorry for us going our own way. Go back to your own world and let your gravity pull your breasts down to your knees.' That's what I'd say."

Denison said, "All right. Whenever you get too close to saying that to some Earthie, you come say it to me and you'll feel better."

"You know what? Every once in a while, some Immie suggests that we build an Earth-park on the Moon; some little spot with Earth-plants brought in as seeds or seedlings; maybe some animals. A touch of home - that's the usual expression."

"I take it you're against that,"

"Of course, I'm against it. A touch of whose home? The Moon is our home. An Immie who wants a touch of home had better get back to his home. Immies can be worse than Earthies sometimes."

'Til keep that in mind," said Denison.

"Not you - so far," said Selene.

There was silence for a moment and Denison wondered if Selene were going to suggest a return to the caverns. On the one hand, it wouldn't be long before he would feel a fairly strenuous craving to visit a rest-room. On the other, he had never felt so relaxed. He wondered how long the oxygen in his pack would hold out

Then Selene said, "Ben, do you mind if I ask you a question?"

"Not at all. If it's my private life that interests you, I am without secrets. I'm five-foot-nine, weigh twenty-eight pounds on the Moon, had one wife long ago, now divorced, one child, a daughter, grown-up and married, attended University of - "

"No, Ben. I'm serious. Can I ask about your work?"

"Of course you can, Selene. I don't know how much I can explain to you, though."

"Well -  You know that Barron and L - M

"Yes, I know," said Denison, brusquely.

"We talk together. He tells me things sometimes. He said you think the Electron Pump might make the Universe explode."

"Our section of the Universe. It might convert a part of our Galactic arm into a quasar."

"Really? Do you really think so?"

Denison said, "When I came to the Moon, I wasn't sure. Now I am. I am personally convinced that this will happen."

"When do you think it will happen?"

"That I can't say exactly. Maybe a few years from now. Maybe a few decades."

There was a short silence between them. Then Selene said, in a subdued voice, "Barron doesn't think so."

"I know he doesn't. I'm not trying to convert him. You don't beat refusal to believe in a frontal attack. That's Lamont's mistake."

"Who's Lamont?"

"I'm sorry, Selene. I'm talking to myself."

"No, Ben. Please tell me. I'm interested. Please."

Denison turned to one side, facing her. "All right," he said. "I have no objection to telling you. Lamont, a physicist back on Earth, tried in his way to alert the world to the dangers of the Pump. He failed. Earthmen want the Pump; they want the free energy; they want it enough to refuse to believe they can't have it."

"But why should they want it, if it means death?"

"All they have to do is refuse to believe it means death. The easiest way to solve a problem is to deny it exists. Your friend, Dr. Neville, does the same thing. He dislikes the surface, so he forces himself to believe that Solar batteries are no good - even though to any impartial observer they would seem the perfect energy source for the Moon. He wants the Pump so he can stay underground, so he refuses to believe that there can be any danger from it."

Selene said, "I don't think Barron would refuse to believe something for which valid evidence existed. Do you really have the evidence?"

"I think I do. It's most amazing really, Selene. The whole thing depends on certain subtle factors of quark-quark interactions. Do you know what that means?"

"You don't have to explain. I've talked so much to Barron about all sorts of things that I might be able to follow."

"Well, I thought I would need the Lunar proton synchrotron for the purpose. It's twenty-five miles across, has superconducting magnets, and can dispose of energies of 20,000 Bev and more. It turns out, though, that you people have something you call a Pionizer, which fits into a moderately sized room and does all the work of the synchrotron. The Moon is to be congratulated on a most amazing advance."

"Thank you," said Selene, complacently. "I mean on behalf of the Moon."

"Well, then, my Pionizer results can show the rate of increase of intensity of strong nuclear interaction; and the increase is what Lamont says it is and not what the orthodox theory would have it be."

"And have you shown it to Barron?"

"No, I haven't. And if I do, I expect Neville to reject it. He'll say the results are marginal. He'll say I've made an error. He'll say that I haven't taken all factors into account. He'll say I've used inadequate controls . . . What he'll really be saying is that he wants the Electron Pump and won't give it up."

"You mean there's no way out."

"Of course there is, but not the direct way. Not Lamont's way."

"What's that?"

"Lamont's solution is to force abandonment of the Pump, but you can't just move backward. You can't push the chicken back into the egg, wine back into the grape, the boy back into the womb. If you want the baby to let go of your watch, you don't just try to explain that he ought to do it - you offer him something he would rather have."

"And what's that?",

"Ah, that's where I'm not so sure. I do have an idea, a simple idea - perhaps too simple to work - based on the quite obvious fact that the number two is ridiculous and can't exist."

There was a silence that lasted for a minute or so and then Selene, her voice as absorbed as his, said, "Let me guess your meaning."

"I don't know that I have any," said Denison.

"Let me guess, anyway. It could make sense to suppose that our own Universe is the only one that can exist or does exist, because it is the only one we live in and directly experience. Once, however, evidence arises that there is a second Universe as well, the one we call the para-Universe, then it becomes absolutely ridiculous to suppose that there are two and only two Universes. If a second Universe can exist, then an infinite number can. Between one and the infinite in cases such as these, there are no sensible numbers. Not only two, but any finite number, is ridiculous and can't exist."

Denison said, "That's exactly my reas - " And silence fell again.

Denison heaved himself into a sitting position and looked down on the suit-encased girl. He said, "I think we had better go back to town."

She said, "I was just guessing."

He said, "No, you weren't. Whatever it was, it wasn't just guessing."