"They don't show much detail."

"No. The light is too much bent by gravitational fields and solar wind and intervening dust and gasses. Our telescopes cannot find further detail."

"So you haven't really learned much."

"I would say that we have learned a good deal. One puzzling point. The ring apparently stops on the close order of 40 percent of neutrinos."

Teela merely looked bewildered; but Speaker made a startled sound, and Louis whistled very low.

That eliminated everything.

Normal matter, even the terrifically compressed matter in the heart of a star, would stop almost no neutrinos. Any neutrino stood a fifty-fifty chance of getting through several light years' thickness of lead.

An object in a Slaver stasis field reflected all neutrinos. So did a General Products hull.

But nothing known would stop 40 percent of neutrinos, and let the rest through.

"Something new, then." said Louis. "Chiron, how big is this ring? How massive is it?"

"The ring masses two times ten to the thirtieth power in grams, measures .95 times ten to the eighth power miles in radius, and something less than ten to the sixth power miles across."

Louis was not comfortable thinking in abstract powers of ten. He tried to translate the numbers into pictures.

He had been right to think of inch-wide Christmas ribbon, balanced on edge and strung in a loop. The ring was more than ninety million miles in radius — about six hundred million miles long, he estimated — but less than a million miles across, edge to edge. It massed a little more than the planet Jupiter …

"Somehow that doesn't seem massive enough," he said. "Something that big should weigh as much as a good sized sun."

The kzin agreed. "One has the ludicrous picture of millions of beings trying to live on a construct no thicker than bookfilm."

"Your intuition is wrong," said the puppeteer with silver curls. "Consider the dimensions. If the ring were a ribbon of hullmetal, for example, it would be approximately fifty feet thick."

Fifty feet? That was hard to believe.

But Teela's eyes had been turned to the ceiling, and her lips had been moving silently but rapidly. "He's right," she said. "The math works out. But what's it for? Why would anyone build such a thing?"

"Room."

"Room?"

"Room to live," Louis amplified. "That's what it's all about. Six hundred trillion square miles of surface area is three million times the surface area of the Earth. It'd be like having three million worlds all mapped flat and joined edge to edge. Three million worlds within aircar distance. That'd solve any population problem.

"And what a problem they must have had! You don't go into a project like that one just for kicks."

"A point," said the kzin. "Chiron, have you searched neighboring stars for other, similar rings?"

"Yes, we -"

"And found none. As I thought. If the race that built the ring had known of faster-than-light travel, they would have settled other stars. They would not have needed the ring. Therefore there is only one ring."

"Yes."

"I am reassured. We are superior to the ringmakers in at least one respect." The kzin stood suddenly. "Are we to explore the habitable surface of the ring?"

"A physical landing might prove to be overambitious."

"Nonsense. We must inspect the vehicle you have prepared for us. Is its landing gear sufficiently versatile? When may we depart?"

Chiron whistled, a startled burst of discord. "You must be mad. Consider the power of those who built this ring! They make my own civilization seem savages!"

"Or cowards."

"Very well. You may go to inspect your craft when the one you call Nessus returns. For the time previous to that event, there are more data regarding the ring."

"You try my patience," said Speaker. But he sat down.

You liar, thought Louis. You take it well, and I'm proud of you. His own stomach was queasy as he returned to his couch. A baby blue ribbon stretched across the stars; and man had met superior beings — again.

The kzinti had been first.

When men first used fusion drives to cross the gaps between the stars, the kzinti were already using the gravity polarizer to power their interstellar warships. It made their ships faster and more maneuverable than human ships.

Man's resistance to the kzinti fleet would have been nominal, had it not been for the Kzinti Lesson: A reaction drive is a weapon devastating in direct proportion to it's efficiency as a drive.

Their first foray into human space had been a terrific shock to the kzinti. Human society had been peaceful for centuries, for so long that they had virtually forgotten war. But human interstellar ships used fusion-powered photon drives, launched by a combination of photon sail and asteroid-based laser cannon.

So the kzinti telepathe continued to report that the human worlds had no weapons at all … while giant laser cannon chopped at the kzinti ships, and smaller mobile cannon darted in and out on the light pressure of their own beams …

Slowed by unexpected human resistance and by the barrier of lightspeed, the war had run for decades instead of years. But the kzinti would have won eventually.

Except that an Outsider ship had stumbled across the small human colony on We Made It. They had sold the mayor the secret of the Outsider hyperdrive shunt, on credit. We Made It had not known of the kzinti war; but they learned of it fast enough when they had built a few faster-than-light ships.

Against hyperdrive the kzinti hadn't a prayer.

Later, the puppeteers had come to set up trading posts in human space …

Man had been very lucky. Three times he had met races technologically superior to him. The kzinti would have crushed him without the Outsider hyperdrive. The Outsiders, again, were clearly his superiors; but they wanted nothing that man could give them, except supply bases and information, and these they could buy. In any case the Outsiders, fragile beings of Helium II metabolism, were too vulnerable to heat and gravity to make good warriors. And the puppeteers, powerful beyond dreams, were too cowardly.

Who had built the Ringworld? And … were they warriors?

Months later, Louis was to see Speaker's lie as his personal turning point. He might have backed out then — on Teela's behalf, of course. The Ringworld was terrifying enough as an abstraction in numbers. To think of approaching it in a spacecraft, of landing on it …

But Louis had seen the kzin in terror of the puppeteers' flying worlds. Speakees lie was a magnificent act of courage. Could Louis show himself a coward now?

He sat down and turned to face the glowing projection; and as his eyes brushed Teela he silently cursed her for an idiot. Her face was alive with wonder and delight. She was as eager as the kzin pretended to be. Was she too stupid to be afraid?

There was an atmopshere on the ring's inner side. Spectroanalysis showed the air to be as thick as Earth's, and of approximately the same composition: definitely breathable to man and kzin and puppeteer. What kept it from blowing away was a thing to be guessed at. They would have to go and look.

In the system of the G2 sun there was nothing at all but the ring itself. No planets, no asteroids, no comets.

"They cleaned it out," said Louis. "They didn't want anything to hit the ring."

"Naturally," said the puppeteer with silver curls. "If something did strike the ring, it would strike at a minimum of 770 miles per second, the speed of rotation of the ring itself. No matter how strong the material of the ring, there would always be the danger of an object missing the outer surface and crossing the sun to strike the unprotected, inhabited inner surface."

The sun itself was a yellow dwarf somewhat cooler than Sol and a touch smaller. "We will need heat suits on the ring," said the kzin — rubbing it in, Louis thought.