From the control room Speaker-to-Animal snarled something complicated, a sound powerful enough to curse the very air of the cabin. Teela giggled.

"If the puppeteers have been thinking along the same lines as Dyson," Louis continued, "they might very well expect to find the Clouds of Magellan riddled with Ringworlds, edge to edge."

"And that's why we were called in."

"I'd hate to bet on a puppeteer's thoughts. But if I had to, that's the way I'd bet."

"No wonder you've been spending all your time in the library."

"Infuriating!" screamed the kzin. "Insulting! They deliberately ignore us! They pointedly turn their backs to invite attack!"

"Improbable," said Nessus. "If you cannot find radio transmissions, then they do not use radio. Even if they were routinely using radio lasers, we would detect some leakap."

"They do not use lasers, they do not use radio, they do not use hyperwave. What are they using for communicadon? Telepathy? Wntten messages? Big mirrors?"

"Parrots," Louis suggested. He got up to join them at the door to the control room. "Huge parrots, specially bred for their oversized lungs. They're too big to fly. They just sit on hilltops and scream at each other."

Speaker turned to look Louis in the eye. "For four hours I have tried to contact the Ringworld. For four hours the inhabitants have ignored me. Their contempt has been absolute. Not a word have they vouchsafed me. My muscles are trembling for lack of exercise, my fur is matted, my eyes refuse to focus, my sthondat-begotten room is too small, my microwave heater heats all meat to the same temperature, and it is the wrong temperature, and I cannot get it fixed. Were it not for your help and your suggestions, Louis, I would despair."

"Can they have lost their civilization?" Nessus mused. "It would be silly of them, considering."

"Perhaps they are dead," Speaker said viciously. "That too would be silly. Not to contact us has been silly. Let us land and find out."

Nessus whistled in panic. "Land on a world which may have killed its indigenous species? Are you mad?"

"How else can we learn?"

"Of course," Teela chimed in. "We didn't come all this way just to fly in circles!"

"I forbid it. Speaker, continue your attempts to contact the Ringworld."

"I have ended such attempts."

"Repeat them."

"I will not."

In stepped Louis Wu, volunteer diplomat. "Cool it, furry buddy. Nessus, he's right. The Ringworlders don't have anything to say to us. Otherwise we'd know it by now."

"But what can we do other than keep trying?"

"Go on about our business. Give the Ringworlders time to make up their minds about us."

Reluctantly the puppeteer agreed.

They drifted toward the Ringworld.

Speaker had aimed the Liar to pass outside the Ringworld's edge: a concession to Nessus. The puppeteer feared that hypothetical Ringworlders would take it as a threat if the ship's course should intersect the ring itself. He also claimed that fusion drives of the Liar's power had the look of weapons; and so the Liar moved on thrusters alone.

To the eye there was no way of judging scale. Over the hours the ring shifted position. Too slowly. With cabin gravity to compensate for from zero to thirty gee of thrust, the inner ear could not sense motion. Time passed in a vacuum, and Louis, for the first time since leaving Earth, was ready to gnaw his fingernails.

Finally the ring was edge-on to the Liar. Speaker used the thrusters, braking the ship into a circular orbit around the rim; and then he sent them drifting in toward the

Now there was motion.

The rim of the Ringworld grew from a dim line occluding a few stars, to a black wall. A wall a thousand miles high, featureless, though any features would have been blurred by speed. Half a thousand miles away, blocking ninety degrees of sky, the wall sped past at a hellish 770 miles per second. Its edges converged to vanishing points, to points at infinity at either end of the universe; and from each point at infinity, a narrow line of baby blue shot straight upward.

To look into the vanishing point was to step into another universe, a universe of true straight lines, right angles, and other geometric abstractions. Louis stared hypnotized into the vanishing point. Which point was it, the source or the sink? Did the black wall emerge or vanish in that meeting place?

… from out of the point at infinity, something came at them.

It was a ledge, growing like another abstraction along the base of the rim wall. First the ledge appeared; then, mounted on the ledge, a row of upright rings. Straight at the Liar they came, straight at the bridge of Louis's nose. Louis shut his eyes and threw his arms up to protect his head. He heard a whimper of fear.

Death should have come in that instant. When it didn't, he opened his eyes. The rings were going by in a steady stream; and he realized that they were no more than fifty miles across.

Nessus was curled in a ball. Teela, her palms pressed flat against the transparent hull, was staring avidly outward. Speaker was fearless and attentive at the control board. Perhaps he was better than Louis at judging distance.

Or perhaps he was faking it. The whimper could have come from Speaker.

Nessus uncurled. He looked out at the rings, which were smaller now, converging. "Speaker, you must match velocities with the Ringworld. Hold us in position by thrusting at one gravity. We must inspect this."

Centrifugal force is an illusion, a manifestation of the law of inertia. Reality is centripetal force, a force applied at right angles to the velocity vector of a mass. The mass resists, tends to move in its accustomed straight line.

By reason of its velocity and the law of inertia, the Ringworld tended to fly apart. Its rigid structure would not allow that. The Ringworld applied its own centrifugal force to itself. The Liar, matching speed at 770 miles per second, had to match that centripetal force.

Speaker matched it. The Liar hovered next to the rim wall, balanced on .992 gee of thrust, while her crew inspected the spaceport.

The spaceport was a narrow ledge, so narrow as to be a dimensionless line until Speaker moved the ship inward. Then it was wide, wide enough to dwarf a pair of tremendous spacecraft. Ile craft were flat nosed cylinders, both of the same design: an unfamiliar design, yet clearly the design of a fusion-ramship. These ships were intended to fuel themselves, picking up interstellar hydrogen in scoops of electromagnetic force. One had been cannibalized for parts, so that it stood with its guts open to vacuum and its intimate structure exposed to alien eyes.

Windows showed around the upper run of the intact ship, allowing those eyes to gauge that ship's size. In the random starlight, the glitter of windows was precisely like crystal candy sprinkled on a cake. Thousands of windows. That ship was big.

And it was dark. The entire spaceport was dark. Perhaps the beings who used it did not need light in the "visible" frequencies. But to Louis Wu, the spaceport looked abandoned.

"I don't understand the rings," said Teela.

"Electromagnetic cannon," Louis answered absently. "For takeoffs."

"No," said Nessus.

"Oh?"

"The cannon must have been intended for landing the ships. One can even surmise the method used. The ship must go into orbit alongside the rim wall. It will not attempt to match the ring's velocity, but will position itself twenty-five miles from the base of the rim wall. As the ring rotates, the coils of the electromagnetic cannon will scoop up the ship and accelerate it to match the velocity of the ring. I compliment the ring engineers. The ship need never come close enough to the ring to be dangerous."