"We know that we have no undying part," said Nessus. "I will not speak for your race. I have not the right. My species has no immortal part. Our scientists have proved this. We are afraid to die, for we know that death is permanent."

"And?"

"Ships disappear in the Blind Spot. No puppeteer would go too near a singularity in hyperdrive; yet still they disappeared, in the days when our ships carried pilots. I trust the engineers who built the Liar. Hence I trust the cabin gravity. It will not fail us. But even the engineers fear the Blind Spot."

There was a ship's night, during which Louis slept poorly and dreamed spectacularly, and a ships day, during which Teela and Louis found each other impossible to live with. She was not frightened. Louis suspected he would never see her frightened. She was merely bored stiff.

That evening, in the space of half an hour, the ringed star came out from behind the sternward block of living-sleeping cabins. The star was small and white, a shade less intense than Sol, and it nestled in a shallow pencil-line of arc blue.

They stood looking over Speaker's shoulder as Speaker activated the scope screen. He found the arc-blue line of the Ringworld's inner surface, touched the expansion button. One question answered itself amost immediately.

"Something at the edge," said Louis.

"Keep the scope centered on the rim," Nessus ordered.

The rim of the ring expanded in their view. It was a wall, rising inward toward the star. They could see its black, space-exposed outer side silhouetted against the sunlit blue landscape. A low rim wall, but low only in comparison to the ring itself.

"If the ring is a million miles across," Louis estimated, "The rim wall must be at least a thousand miles high. Well, now we know. That's what holds the air in."

"Would it work?"

"It should. The ring's spinning for about a gravity. A little air might leak over the edges over the thousands of years, but they could replace it. To build the ring at all, they must have had cheap transmutation — a few tenth-stars per kiloton — not to mention a dozen other impossibilities."

"I wonder what it looks like from the inside."

Speaker heard, and he touched a control point, and the view slid. The magnification was not yet great enough to pick up details. Bright blue and brighter white slid across the scope screen, and the blurred straight edge of a navy blue shadow …

The further rim slid into view. Here the rim wall was tilted outward.

Nessus, standing in the doorway with his heads poised above Speaker's shoulders, ordered, "Give us what magnification you can."

The view expanded.

"Mountains," said Teela. "How lovely." For the rim wall was irregular, sculptured like eroded rock, and was the color of the Moon. "Mountains a thousand miles high."

"I can expand the view no further. For greater detail we must approach closer."

"Let us first attempt to contact them," said the puppeteer. "Are we at rest?"

Speaker consulted the ship's brain. "We are approaching the primary at perhaps thirty miles per second. Is that slow enough?"

"Yes. Begin transmissions."

No laser light was falling on the Liar.

Testing for electromagnetic radiation was more difficult. Radio, infrared, ultraviolet, X-rays — the whole spectrum had to be investigated, from the room-temperature heat given off by the dark side of the Ringworld, up to light quanta energetic enough to split into matter-antimatter pairs. The twenty-one centimeter band was empty; and so were its easy multiples and divisors, which might have been used merely because the hydrogen absorption band was so obvious. Beyond that point Speaker-To-Animals was playing blind man's bluff with his receivers.

The great pods of communications equipment on the Liar's wing had opened. The Liar was sending radio messages on the hydrogen absorption frequency and others, bathing successive portions of the ring's inner surface with laser light of ten different frequencies, and sending Interworld-Morse in alternate blasts of the fusion motors.

"Our autopilot would eventually translate any possible message," said Nessus. "We must assume that their ground-based computers are at least as capable.

Speakees reply was venomous. "Can your leucotomized computers translate total silence?"

"Concentrate your sendings at the rim. If they have spaceports, the spaceports must be at the rim. To land a spacecraft anywhere else would be horribly dangerous."

In the Hero's Tongue Speaker-To-Animals snarled something horribly insulting. Effectively it ended the conversation; but Nessus stayed where he had been for hours now, with his heads poised alertly above the kzin's shoulders.

The Ringworld waited beyond the hull, a checkered blue ribbon trailing across the sky.

"You tried to tell me about Dyson spheres," said Teela.

"And you told me to go pick lice out of my hair." Louis had found a description of Dyson spheres in the ship's library. Excited by the idea, he had made the mistake of interrupting Teela's game of solitaire to tell her about it.

"Tell me now," she coaxed.

"Go pick lice out of your hair."

She waited.

"You win," said Louis. For the past hour he had been staring broodingly out at the ring. He was as bored as she was.

"I tried to tell you that the Ringworld is a compromise, an engineering compromise between a Dyson sphere and a normal planet.

"Dyson was one of the ancient natural philosophers, pre-Belt, almost pre-atomic. He pointed out that a civilization is limited by the energy available to it. The way for the human race to use all the energy within its reach, he said, is to build a spherical shell around the sun and trap every ray of sunlight.

"Now if you'll quit giggling for just a minute, you'll see the idea. The Earth traps only about half a billionth of the sun's output. If we could use all that energy …

"Well, it wasn't crazy then. There wasn't even a theoretical basis for faster-than-light travel. We never did invent hyperdrive, if you'll recall. We'd never have discovered it by accident, either, because we'd never have thought to do our experiments out beyond the singularity.

"Suppose an Outsider ship hadn't stumbled across a United Nations ramrobot? Suppose the Fertility Laws hadn't worked out? With a trillion human beings standing on each other's shoulders, and the ramships the fastest thing around, how long could we get along on fusion power? We'd use up all the hydrogen in Earth's oceans in a hundred years.

"But there's more to a Dyson sphere than collecting solar power.

"Say you make the sphere one astronomical unit in radius. You've got to clear out the solar system anyway, so you use all the solar planets in the construction. That gives you a shell of, say, chrome steel a few yards thick. Now you put gravity generators all over the shell. You'd have a surface area a billion times as big as the Earth's surface. A trillion people could wander all their lives without ever meeting one another."

Teela finlly got a full sentence in edgewise. "You're using the gravity generators to hold everything down?"

"Yeah, against the inside. We cover the inside with soil."

"What if one of the gravity generators broke down?"

"Picky, picky, picky. Well … you'd get a billion people drifting up into the sun. All the air swarming up after them. A tornado big enough to swallow the Earth. Not a prayer of getting a repair crew in, not through that kind of a storm …"

"I don't like it," Teela said decisively.

"Let's not be hasty. There may be ways to make a gravity generator foolproof."

"Not that. You couldn't see the stars."

Louis hadn't thought of that aspect. "Never mind. The point about Dyson spheres is that any sentient, industrial race is eventually going to need one. Technological civilizations tend to use more and more power as time goes on. The ring is a compromise between a normal planet and a Dyson sphere. With the ring you get only a fraction of the available room, and you block only a fraction of the available sunlight; but you can see the stars, and you don't have to worry about gravity generators."